Chapter No.1: Chemical Equilibrium -Chemistry For Class X (2022 and Onward) - Text Book Exercises ( Section "B" & "C" and Test Yourself)

Go To Index
Chemical Equilibrium
Text Book Exercises

SECTION- B: SHORT QUESTIONS

1. Define chemical equilibrium with example.
Ans: Chemical Equilibrium:
The reversible chemical reaction never goes to completion because product reacts and reproduce reactants again and take place in forward and reverse direction. This state in which forward reaction rate and reverse reaction rate are equal known as equilibrium.
Equilibrium means a 'balance'. Equilibrium exists in many ways in our surroundings.
"It is a state where the rate of the forward reaction is equal to the rate of backward reaction."

OR

It is also defined as "A state where the concentration of reactant and product remains constant."
Example:

H_2(g) + I_2(g) ⇌ 2HI_(g)

2. Why chemical equilibrium is dynamic?
Ans: Chemical Equilibrium Is Dynamic:
We know that chemical equilibrium can be written by general equation as:

aA + bB ⇌ cC + dD

The reaction rate depends on the concentration of the reactants. At the beginning the quantity of reactant is higher, and the rate of forward reaction is higher.
Forward rate:

R_f = K_f [A]^a [B]^b

As the product is formed, the reverse reaction is then able to occur.
Backward rate:

R_r = K_r [C]^c [D]^d

As the reactant amount decreases, the rate of reactant transformation also decreases, and the rate of product formation decreases. After a certain time, the concentrations of reactants and products become constant, and equilibrium is established.

Rate of forward reaction = Rate of reverse reaction
R_f = R_r
K_f [A]^a [B]^b = K_r[C]^c [D]^d

Upon arrangement,

Where Kc is called equilibrium constant for the reaction.
The rate of both forward and reverse reaction becomes equal upon reaching the equilibrium point. So, there is no observable changes although both forward and reverse reactions occurring. The reaction has not stopped. Hence, it has proved that chemical equilibrium is dynamic in nature.

3. When writing an equation, how is a reversible reaction distinguished from irreversible reaction?
Ans: In writing an equation irreversible reaction is written with single right headed arrow (→). While reversible reaction means the products also react with each other and become reactant once again, so we write it with double half headed arrows (⇌) with opposite directions. The right arrow is represnting the reaction from reactant to product and the left arrow represents the reaction from products to reactant.

OR

In other words,
The direction of a reaction can be predicted by type of arrow; single headed arrow (→) used for irreversible reactions and a double half headed arrows (⇌)are used for reversible reaction, that never goes to completion.

4. Write an equilibrium equation of monatomic carbon and a molecule of oxygen as reactant and carbon monoxide as product.
Ans: EQUATION

 2C_s + O_2(g) ⇌ 2CO_(g)

5. Outline the characteristics of reversible reaction.
Ans: CHARACTERISTICS OF REVERSIBLE REACTION:

• It is always directed from right to left in a chemical reaction.
• Product produce reactant (Reactants ← Products).
• Initially rate is slow but gradually speed up.
• Reversible reactions always attain equilibrium and never proceed to completion under certain condition of temperature and pressure.
• Dynamic equilibrium is established.

6. Distinguished between reversible and irreversible reaction.
Ans: Difference Between Reversible And Irreversible Reaction

S.No.	Reversible Reaction	Irreversible Reaction
1.	It can reverse in suitable condition.	It can reverse in suitable condition.
2.	Both forward and backward reactions take place simultaneously.	It is unidirectional, it proceeds only in a forward direction.
3.	It attains equilibrium.	equilibrium is not attained.
4.	The reactant can not be converted completely into products.	The reactant can be converted completely into products.
5.	It is relatively slow.	It is fast
6.	Double half headed arrows (⇌)are used for reversible reaction	Single headed arrow (→) used for irreversible reactions

7. State law of mass action. How is the active mass is represented?
Ans: LAW OF MASS ACTION:
Statement:
The law of mass action state that:

"The rate of a reaction is directly proportional to the product of the concentration of each reactant."

REPRESENTATION OF ACTIVE MASS:
The concentration of reacting substance is called Active mass. The unit of active mass is mol and its value is expressed in square brackets [ ].
Example: [O₂] = 0.127 mol.dm^-3

8. Why equilibrium constant may or may not have unit? Justify with example.
Ans: Unit Of Equilibrium Constant:
At Equilibrium Position  Equilibrium Constant Has No Unit:

Rate of the forward reaction = Rate of the backward reaction

An equal number of moles on both sides of the equation has no unit in K_c, because K_c expression uses concentration units that cancel. The unit of concentration is mol.dm^-3.
Consider a reaction:

CO_2(g) + H_2(g) ⇌ CO_(g) + H₂O_(g)

If Reactant And Products Concentration Are Not Equal K_c has unit:
For reactions when the number of moles of reactants and product are not equal, K_c has a unit. Let us consider the following reaction:

N_2(g) + 3H_2(g) ⇌ 2NH_3(g)

9. How direction of a reaction can be predicted if K_c is known to you.
Ans: Direction Of A Chemical Reaction:
When dealing with reversible reactions, it is critical to determine the reaction's direction at any given time. The reaction quotient, Q_c, can help make such predictions.
Under non-equilibrium condition, reaction quotient 'Q_c' is define as the ratio of the product of active masses of reactant and products raised to the respective stoichiometric coefficients in the balanced chemical equation to that of the reactant.
It has the some mathematical structure as K_c. Comparing K_c and Q_c values predicts reactions direction. We have three categories:

1. If Q_c = K_c:
   The actual product and reactant concentrations are equal to the equilibrium concentrations, and the system is stable.
2. If Q_c < K_c:
   Then there is increase in product concentration for equilibrium. So the forward reaction occurs, forming additional products.
3. If Q_c > K_c:
   There is decrease in product concentration & to achieve equilibrium. As, the process reverses, forming more reactants.

10. Write equilibrium constant expression for the following equations:
i) N₂ + 2O₂ ⇌ 2NO₂
ii) N₂ + H₂ ⇌ 2NH₃
iii) H₂ + Br₂ ⇌ 2HBr

Ans: i) N₂ + 2O₂ ⇌ 2NO₂

ii) N₂ + H₂ ⇌ 2NH₃

iii) H₂ + Br₂ ⇌ 2HBr

SECTION-C: DETAILED QUESTIONS

1. Describe dynamic equilibrium with two examples.
Ans: Dynamic Equilibrium:
The reaction rate depends on the concentration of the reactants. At the beginning the quantity of reactant is higher, and the rate of product formation is the higher. As the reactant amount decreases, the rate of reactant transformation also decreases, and the rate of product formation decreases. After o certain time, the concentrations of reactants and products become constant, and this state is called dynamic equilibrium.

Rate of forward reaction = Rate of reverse reaction

In a reversible reaction, dynamic equilibrium is established before the completion of reaction. The rate of both forward and reverse reaction becomes equal upon reaching the equilibrium point.
Graph:
The following graph which is of concentrations vs. time, shows that the concentrations of both reactants and product becomes constant at equilibrium.

Dynamic Equilibrium

Example No.1: Formation of Hydrogen Iodide
An example of a reaction at equilibrium is a reaction of hydrogen and iodine in a closed container to produce hydrogen iodide. At the start of the reaction, there is a high concentration of hydrogen and iodine and, after that, the concentration decreases as hydrogen iodide is formed. The concentration of hydrogen iodide increases as the forward reaction proceeds. As hydrogen iodide is formed, the reverse reaction is then able to occur.

H_2(g) + I_2(g) ⇌ 2HI_(g)

Hydrogen-Iodine Equilibrium System

So, there is no observable changes although both forward and reverse reactions occurring. The reaction has not stopped but reached dynamic equilibrium.

Example No.2: Formation of Ammonia
Let us take an example of manufacturing of ammonia.When one mole of nitrogen gas reacts with three moles of hydrogen it produces two moles of ammonia gas. This is known as 'Forward reaction'.

N_2(g) + 3H_2(g) → 2NH_3(g)

In contrast, two moles of ammonia gas may also be converted into one mole of nitrogen and three moles of hydrogen. This is known as 'Reverse reaction'.

N_2(g) + 3H_2(g) ← 2NH_3(g)

When both of these reactions are written together as a reversible reaction, they are represented as:

N_2(g) + 3H_2(g) ⇌ 2NH_3(g)

So, there is no observable changes although both forward and reverse reactions occurring. The reaction has not stopped and reached dynamic equilibrium.


2. State law of mass action. Derive an expression for equilibrium constant.
Ans: LAW OF MASS ACTION:
Statement:
The law of mass action state that:

"The rate of a reaction is directly proportional to the product of the concentration of each reactant."

Explanation:
The rate at which a substance reacts is directly proportional to its active mass and the rate of a reaction is directly proportional to the product of the active masses of the reacting substances. The law of mass action also suggests that the ratio of the reactant concentration and the product concentration is constant at a state of chemical equilibrium.

Derivation Of Equation For Equilibrium Constant:
Let us apply law of mass action on a hypothetical reversible reaction.

aA + bB ⇄ cC + dD

Forward Reaction:
First let us discuss forward reaction, where A and B are reactants whereas 'a' and 'b' are number of moles needed to balance a chemical equation. The rate of forward reaction according to law of mass action is:

R_f ∝ [A]^a [B]^b

R_f = K_f [A]^a [B]^b

Where K_f is the rate constant for forward reaction.

Reverse reaction:
Likewise, rate of reverse reaction is directly proportional to product of molar concentrations of C and D whereas 'c' and 'd' are number of moles needed to balance a chemical reaction.

R_r ∝ [C]^c [D]^d

R_r = K_r [C]^c [D]^d

Where K_r is the rate constant for reverse reaction.

At Equilibrium:
We know that, at equilibrium rate of forward and reverse reaction becomes equal. So,

R_f = R_r

Putting the values of R_f and R_r, we have:

K_f [A]^a [B]^b = K_r [C]^c [D]^d

By taking constants on L.H.S and variables on R.H.S, we have

Where K_c is called equilibrium constant.
Hence proven that law of mass action describe relation between active masses of reactants and products with rate of reaction. All the reversible reactions can be expressed in this form.

3. Describe the characteristics of equilibrium constant.
Ans: Characteristics Of Equilibrium Constant Expression

1. Important characteristics of equilibrium constant expression are as follows:
2. K_c only works in equilibrium.
3. It represents the equilibrium concentration of the reactant and product in mol.dm^-3
4. K_c is independent of reactant and product concentrations.
5. K_c varies with temperature.
6. K_c is a balanced chemical equation coefficient. In a balanced chemical equation, each reactant and product has a concentration equal to its coefficient.
7. K_c represents equilibrium position. If K_c is larger than 1, the reaction is forward. If K_c is less than 1, the reaction is a reverse reaction.
8. Equilibrium constant K_c is a ratio of reactant to product that is utilized to define chemical behavior.

4. How can you predict the following stages of a reaction by comparing the values of Kc and Qc.

1. Net reaction proceeds in forward direction.
2. Net reaction proceeds in reverse direction

Ans: i) Net reaction proceeds in forward direction.
If Q_c < K_c:
Then there is increase in product concentration for equilibrium. So the forward reaction occurs, forming additional products.
Example:
In the beginning of reaction, when one mole of nitrogen gas reacts with three moles of hydrogen it produces two moles of ammonia gas. 'Forward reaction' proceed. 

N_2(g) + 3H_2(g) → 2NH_3(g)

ii) Net reaction proceeds in reverse direction
If Q_c > K_c:
There is decrease in product concentration & to achieve equilibrium. As, the process reverses, forming more reactants.
Example:
After formation of ammonia,  two moles of ammonia gas may also be converted into one mole of nitrogen and three moles of hydrogen. 'Reverse reaction' proceed.

N_2(g) + 3H_2(g) ← 2NH_3(g)

5. Predict which system at equilibrium will contain maximum amount of product and which system will contain maximum amount of reactant?

1. 2CO_2(g) ⇌ 2CO_(g) + O_2(g) K_c(927 C) = 3.1x10^-18 mol.dm^-3
2. 2O_3(g) ⇌ 3O_2(g) K_c(298K) = 5.9 x 10⁵⁵ mol.dm^-3

Ans: The magnitude of K_c can give us some information about the reactant and product concentrations at equilibrium:

• If K_c is very large, ~1000 or more, we will have mostly product species present at equilibrium.
• If K_c is very small, ~0.001 or less, we will have mostly reactant species present at equilibrium.
• If K_c is between 0.001 and 1000, we will have a significant concentration of both reactant and product species present at equilibrium.

By using these guidelines, we can quickly estimate whether a reaction will:
strongly favour the forward direction to make products → very large K_c, strongly favour the backward direction to make reactants → very small K_c, or somewhere in between.
Therefore, system (b) will contain the maximum amount of product.

TEST YOURSELF

1. Write down forward and reverse reactions for the following.
N_2(g) + O_2(g) ⇌ 2NO
2SO_2(g) + O_2(g) ⇌ 2SO_3(g)
COCl_2(g) ⇌ CO_(g) + Cl_2(g)
Ans: (i)
Forward Reaction: N_2(g) + O_2(g) ⟶ 2NO
Reverse Reaction: N_2(g) + O_2(g) ← 2NO

(ii)
Forward Reaction: 2SO_2(g) + O_2(g) ⟶ 2SO_3(g)
Reverse Reaction: 2SO_2(g) + O_2(g) ← 2SO_3(g)

(iii)
Forward Reaction: COCl_2(g) ⟶ CO_(g) + Cl_2(g)
Reverse Reaction: COCl_2(g) ← CO_(g) + Cl_2(g)

2. Define the term active mass?
Ans: ACTIVE MASS:
The concentration of reacting substance is called Active mass.
Unit:
The unit of active mass is mol.dm-3 or mol/L and its value is expressed in square brackets.

3. Figure out coefficients for given hypothetical reaction.

9X_(g) + Y_3(g)`⇌ 3X₃Y_(g)

Ans: Coefficients Of X = 9
Coefficients Of Y₃ = 1
Coefficients Of X₃Y = 3

4. Write down K_c equation for given reaction:

• S_(s) + O_2(g) ⇌ SO_2(g)
• SO_2(g) + NO_2(g) ⇌ NO_(g) + SO_3(g)
• NH₄Cl_s ⇌ NH_3(g) + HCl_(l)

Ans: K_c Equation:
(i) S_(s) + O_2(g) ⇌ SO_2(g)

(ii) SO_2(g) + NO_2(g) ⇌ NO_(g) + SO_3(g)

(iii) NH₄Cl_s ⇌ NH_3(g) + HCl_(l)

5. The value of K_c for the following reaction at 717K is 48.

H_2(g) + I_2(g) ⇌ 2HI_(g)

At a particular instant, the concentration of H₂, I₂ and HI are found to be 0.2 molL^-1, 0.2 molL^-1, and 0.6 molL^-1 respectively. Calculate reaction quotient for given reaction. Also predict direction of reaction.
Ans: Solution:
Given:

• K_c = 48 at 717K
• [H₂] = 0.2 molL^-1
• [I₂] = 0.2 molL^-10.2 molL^-1
  
• [HI] = 0.6 molL^-1

Working Formula:
At a given time the reaction quotient Q_c for given reaction will be given by the expression:

Therefore Q_c < K_c
Ans: Q_c < K_c, so reaction will proceed in forward direction.

6. Match each of the following statement with appropriate diagram.

Ans: A- (ii) , B- (i), C- (iii)

Do You Know

Q.1: How equilibrium occurs in our Body?
Ans: Equilibrium in our Body:
Equilibrium is present in our bodies. Haemoglobin is macromolecule that transports oxygen around our bodies. Without it we would not survive. The haemoglobin has to be able to take up oxygen, but also to release it and this Is done through changes in the chemical equilibrium of this reaction in different places in our bodies.

Q.2: In which groups equilibrium constant exist?
Ans: Equilibrium constants exist for certain groups of equilibria, such as for weak acids, weak bases, the autoionization of water, and slightly soluble salts.

Q.3: Write down few lines about society, technology and science.
Ans: Society, Technology and Science:
The atmosphere is composed of nitrogen, oxygen, carbon dioxide, methane, nitrous oxide and ozone but the nitrogen and oxygen gases are the most important port of the atmosphere. They are 99% of the atmosphere and use to manufacture chemicals such as nitrogen is used for preparation of ammonia and ammonia is used to prepare nitrogenous fertilizers. Oxygen is used for preparation of sulphur dioxide and sulphur dioxide is used to prepare sulphuric acid.

Chapter No.1: Chemical Equilibrium -Chemistry For Class X (2022 and Onward) - Question & Answers

Go To Index
Chemical Equilibrium
Short & Detailed Answer Questions

Q.1: What do you know about chemical reactions?
Ans: Chemical Reactions:
Many physical and chemical changes are occurring in our surroundings which may be due to chemical reactions. In these reactions reactants are converted into one or more products.
A chemical reaction is a chemical change which involves reactants and products
A chemical reaction contains two quantities; reactant and product which are separated by an arrow.
For example:

• The formation of water from hydrogen gas and oxygen gas.
• The decomposition reaction of sodium bicarbonate into sodium carbonate, water, and carbon dioxide etc.

Types Of Chemical Reaction:
The reactions may be:

1. Reversible
   (a) condensation
   (b) evaporation
   (c) freezing
   (d) melting
2. Irreversible
   (a) Combustion
   (b) rusting

Q.2: Define chemical equilibrium in terms of  reversible reaction with example.
Ans: Chemical Equilibrium:
The reversible chemical reaction never goes to completion because product reacts and reproduce reactants again and take place in forward and reverse direction. This state in which forward reaction rate and reverse reaction rate are equal known as equilibrium.
Equilibrium means a 'balance'. Equilibrium exists in many ways in our surroundings.
"It is a state where the rate of the forward reaction is equal to the rate of backward reaction."

OR

It is also defined as "A state where the concentration of reactant and product remains constant."
Example:

H_2(g) + I_2(g) ⇌ 2HI_(g)

Q.3: Give an example of a reversible reaction which never complete and exist in forward and reverse direction?
Ans: An example of a reaction which never complete and exist in forward and reverse directions is the conversion of ice into water by melting and conversion of water into ice by freezing. It is an example of reversible reaction.

Changing Of State Of Reversible Reaction

Q.4: How can the direction of the reaction be predicted from equation?
Ans: Direction Of Reaction:
The direction of a reaction can be predicted by type of arrow; single headed arrow (→) used for irreversible reactions and a double half headed arrows (⇌) are used for reversible reaction, that never goes to completion.

Q.5: Describe a reversible reaction with an example.
Ans: Reversible Reaction:
A reversible reaction never goes to completion. It containing two processes; forward and reverse. Hence, a reversible reaction can move in either direction depends upon conditions.
Example:
Let us take an example of manufacturing of ammonia.
Forward Reaction: When one mole of nitrogen gas reacts with three moles of hydrogen it produces two moles of ammonia gas. This is known as 'Forward reaction'.

N_2(g) + 3H_2(g) → 2NH_3(g)

Reverse Reaction: In contrast, two moles of ammonia gas may also be converted into one mole of nitrogen and three moles of hydrogen. This is known as 'Reverse reaction'.

N_2(g) + 3H_2(g) ← 2NH_3(g)

When both of these reactions are written together as a reversible reaction, they are represented as:

N_2(g) + 3H_2(g) ⇌ 2NH_3(g)

The original laboratory apparatus designed by Fritz Haber and Robert Le Rossignol in 1908 for synthesizing ammonia Equilibrium exists in many ways in our

Q.6: Explain dynamic equilibrium with an example.
Ans: Dynamic Equilibrium:
The reaction rate depends on the concentration of the reactants. At the beginning the quantity of reactant is higher, and the rate of product formation is the higher. As the reactant amount decreases, the rate of reactant transformation also decreases, and the rate of product formation decreases. After o certain time, the concentrations of reactants and products become constant, and this state is called dynamic equilibrium.

Rate of forward reaction = Rate of reverse reaction

In a reversible reaction, dynamic equilibrium is established before the completion of reaction. The rate of both forward and reverse reaction becomes equal upon reaching the equilibrium point.
Graph:
The following graph which is of concentrations vs. time, shows that the concentrations of both reactants and product becomes constant at equilibrium.

Dynamic Equilibrium

Example:
An example of a reaction at equilibrium is a reaction of hydrogen and iodine in a closed container to produce hydrogen iodide. At the start of the reaction, there is a high concentration of hydrogen and iodine and, after that, the concentration decreases as hydrogen iodide is formed. The concentration of hydrogen iodide increases as the forward reaction proceeds. As hydrogen iodide is formed, the reverse reaction is then able to occur.

H_2(g) + I_2(g) ⇌ 2HI_(g)

Hydrogen-Iodine Equilibrium System

So, there is no observable changes although both forward and reverse reactions occurring. The reaction has not stopped but reached dynamic equilibrium.

Q.7: Describe the macroscopic characteristics of forward and reverse reaction?
Ans: Macroscopic Characteristics Of Forward And Reverse Reaction:
FORWARD REACTION:

1. It is always directed from left to right in a chemical reaction.
2. Reactants produce products( Reactants → Products).
3. Initially rate is fast but gradually slow down.

REVERSE REACTION:

1. It is always directed from right to left in a chemical reaction.
2. Product produce reactant (Reactants ← Products).
3. Initially rate is slow but gradually speed up.

Q.8: What are the macroscopic characteristics of forward and reverse reaction in dynamic equilibrium?
Ans: Macroscopic Characteristics Of Forward And Reverse Reaction In Dynamic Equilibrium:

1. A dynamic equilibrium can only exists in a closed system — neither reactants nor products can enter or leave the system.
2. At equilibrium, the concentrations of reactants and products remain constant.
3. At equilibrium, the forward and reverse reactions are taking place at equal and opposite rates.
4. Equilibrium can be approached from either side of the reaction equation.
5. An equilibrium state can be disturbed and again achieved under the given condition of concentration, pressure, and temperature.

Q.9: What is Active Mass? OR Define active mass? and give its unit.
Ans: ACTIVE MASS:
The concentration of reacting substance is called Active mass.
Unit:
The unit of active mass is mol.dm^-3 or mol/L and its value is expressed in square brackets.

Q.10: Define law of mass action and derive the expression for the equilibrium constant.
Ans: LAW OF MASS ACTION:
Statement:
The law of mass action state that:

"The rate of a reaction is directly proportional to the product of the concentration of each reactant."

Explanation:
The rate at which a substance reacts is directly proportional to its active mass and the rate of a reaction is directly proportional to the product of the active masses of the reacting substances. The law of mass action also suggests that the ratio of the reactant concentration and the product concentration is constant at a state of chemical equilibrium.

Derivation Of Equation For Equilibrium Constant:
Let us apply law of mass action on a hypothetical reversible reaction.

aA + bB ⇄ cC + dD

Forward Reaction:
First let us discuss forward reaction, where A and B are reactants whereas 'a' and 'b' are number of moles needed to balance a chemical equation. The rate of forward reaction according to law of mass action is:

R_f ∝ [A]^a [B]^b

R_f = K_f [A]^a [B]^b

Where K_f is the rate constant for forward reaction.

Reverse reaction:
Likewise, rate of reverse reaction is directly proportional to product of molar concentrations of C and D whereas 'c' and 'd' are number of moles needed to balance a chemical reaction.

R_r ∝ [C]^c [D]^d

R_r = K_r [C]^c [D]^d

Where K_r is the rate constant for reverse reaction.

At Equilibrium:
We know that, at equilibrium rate of forward and reverse reaction becomes equal. So,

R_f = R_r

Putting the values of R_f and R_r, we have:

K_f [A]^a [B]^b = K_r [C]^c [D]^d

By taking constants on L.H.S and variables on R.H.S, we have

Where K_c is called equilibrium constant.
Hence proven that law of mass action describe relation between active masses of reactants and products with rate of reaction. All the reversible reactions can be expressed in this form.

Q.11: Define equilibrium Constant? How can equilibrium constant be determined.
Ans: Equilibrium Constant:
An equilibrium constant is used to show the relation between molar concentration of product and molar concentration of reactant. Or It can be define as the ratio between molar concentration of product to the molar concentration of reactant. It is denoted by K_c.
Equation:

Unit: As K_c is a ratio so it has no unit.
K_c is independent of initial concentration of reactant and product. K_c is temperature dependent.

Determine The equilibrium Constant:
Equilibrium constants are determined by observing the concentrations of each ingredient in a single reaction until it reaches equilibrium and then calculating its numerical value. We have to figure out the ratio of product to reactant concentrations. It is impossible to change a given reaction's equilibrium constant since concentrations are measured at equilibrium, and regardless of initial concentrations.

Q.12: What factors affects the equilibrium constant?
Ans: Factors Affects The Equilibrium Constant:
The temperature is the single factor affecting the equilibrium constant's value.

Q.13: Describe the important characteristics of equilibrium constant expression?
Ans: Characteristics Of Equilibrium Constant Expression

1. Important characteristics of equilibrium constant expression are as follows:
2. K_c only works in equilibrium.
3. It represents the equilibrium concentration of the reactant and product in mol.dm^-3
4. K_c is independent of reactant and product concentrations.
5. K_c varies with temperature.
6. K_c is a balanced chemical equation coefficient. In a balanced chemical equation, each reactant and product has a concentration equal to its coefficient.
7. K_c represents equilibrium position. If K_c is larger than 1, the reaction is forward. If K_c is less than 1, the reaction is a reverse reaction.
8. Equilibrium constant K_c is a ratio of reactant to product that is utilized to define chemical behavior.

Q.14: Describe the units of equilibrium constant?
Ans: Unit Of Equilibrium Constant:
At equilibrium:

Rate of the forward reaction = Rate of the backward reaction

An equal number of moles on both sides of the equation has no unit in K_c, because K_c expression uses concentration units that cancel. The unit of concentration is mol.dm^-3.
Consider a reaction:

CO_2(g) + H_2(g) ⇌ CO_(g) + H₂O_(g)

For reactions when the number of motes of reactants and product are not equal, K_c has a unit. Let us consider the following reaction:

N_2(g) + 3H_2(g) ⇌ 2NH_3(g)

Q.15:Write down the importance of the equilibrium constant?
Ans: Importance Of Equilibrium Constant:
The value of K_c varies depending on the response. K_c isn't only a calculating constant. It affects both the direction and the extent of a chemical reaction.

1. Direction Of A Chemical Reaction:
When dealing with reversible reactions, it is critical to determine the reaction's direction at any given time. For example, to produce ammonia efficiently from nitrogen and hydrogen, we must optimize the process. So it's critical to forecast the reaction's condition at any given time. The reaction quotient, Q_c, can help make such predictions.
It has the some mathematical structure as K_c, but Q_c is a ratio of real concentrations computed at a given moment (not a ratio of equilibrium concentrations). Comparing K_c and Q_c values predicts response direction. We have three categories:

1. If Q_c = K_c:
   The actual product and reactant concentrations are equal to the equilibrium concentrations, and the system is stable.
2. If Q_c < K_c:
   Then there is increase in product concentration for equilibrium. So the forward reaction occurs, forming additional products.
3. If Q_c > K_c:
   There is decrease in product concentration & to achieve equilibrium. As, the process reverses, forming more reactants.

2. Extent Of Chemical Reaction:
At a certain temperature, the extent of a reaction is measured. The magnitude of an equilibrium constant can predict the scope of a chemical reaction. As magnitude may be very high, very low, or moderate, so can be extent of a chemical reaction.

1. K_c is very small:
   Reactions with low K_c never finish. That is, maximum reactant concentration and minimum product concentration. These are called 'reverse or backward responses.
   
   F_2(g) ⇌ 2Fe_(g) K_c = 7.4 x 10^-13 at 227 °C 
   
   
2. K_c is very large:
   Reactions with high K_c values are virtually complete. That is, maximum product concentration and minimum reactant concentration. This type of reaction is known as 'Forward reaction.
   
   2H_2(g) + O_2(g) ⇌ 2H₂O_(g) K_c= 2.4 x 10⁴⁷ at 227°C
   
   
3. K_c is neither very small nor very large:
   Reactions which have moderate value of K_c are considered to be at equilibrium. The concentration of reactants and products is almost same. For example:
   
   N₂O_4(g) ⇌ 2NO_2(g) K_c = 0.36 at 25 °C

Q.16: Define reaction quotient Or Q_c?
Ans: Reaction Quotient Or Q_c
Under non-equilibrium condition, reaction quotient 'Q_c' is define as the ratio of the product of active masses of reactant and products raised to the respective stoichiometric coefficients in the balanced chemical equation to that of the reactant.

Chapter No.1: Chemical Equilibrium -Chemistry For Class X (2022 and Onward) - Multiple Choice Questions, Fill in the blanks, Concept Diagram

Go To Index
Chemical Equilibrium
MULTIPLE CHOICE QUESTIONS (MCQs)

Tick the correct answer from the following:
1. Which one of the following statements is false about dynamic equilibrium?

• It takes place in a close container
• Concentration of reactant and products are not changed
• Rate of forward reaction is equal to rate of reverse reaction
• Equilibrium cannot be disturbed by any external stress ✔

2. Consider the following reaction and indicate which of the following best describe equilibrium constant expression Kc.

4NH₃ + 5O₂ ⇌ 4NO + 6H₂O

3. A reaction which is never goes to completion is known as reversible reaction. Reversible reaction is represented by:

• Doted lines
• Single arrow
• Double arrow ✔
• Double straight line

4. When the magnitude of Kc is small, indicates:

• Reaction mixture contain most of the reactant ✔
• Reaction mixture contain most of the product
• Reaction mixture contain almost equal amount of reactant and product
• Reaction goes to completion

5. For which system does the equilibrium constant, Kc has units of concentration.

• N_2(g) + 3H_2(g) ⇌ 2NH_3(g) ✔
• N_2(g) + 0_2(g) ⇌ 2NO
• H_2(g) +1_2(g) ⇌ 2HI_(g)
• CO_2(g) + H_3(g) ⇌ CO + H₂O_(l)

6. The unit of K_c for reaction N₂ + O₂ ⇌ 2NO

• mol dm^-3
• mol^-2dm⁶
• mol^-1dm³
• no unit ✔

7. The system is stable in equilibrium when:

• Qc = Kc ✔
• Qc > Kc
• Qc < K
• None of these

8. Qc can be defined as:

• ratio of product and reactants
• ratio of molar concentration of product and reactant at specific time ✔
• ratio of molar concentration of product and molar volume of reactant
• ratio of molar concentration of product and reactant raised to the power of coefficient

9. Which of the following represent backward reaction?

• (i) and (ii)
• (ii) and (iii)
• (ii) only
• (iii) only ✔

10. The value of Kc increases when:

• [Product] is less
• [Product] is more ✔
• [Reactant] is more
• [Reactant = product]

11. Which of these are reversible reactions?

• Condensation
• Evaporation
• Both 'a' & 'b' ✔
• None of them

12. Which one is not a reversible reaction?

• Evaporation
• Melting
• Freezing
• Combustion ✔

13. Which reactions are irreversible reactions?
(i) Condensation (ii) Combustion (iii) Melting (iv) Rusting

• (i) & (ii)
• (iii) & (iv)
• (ii) & (iv) ✔
• (i) & (iv)

14. Many physical and chemical changes are occurring in our surrounding which may be due to:

• chemical reaction ✔
• physical reaction
• Both 'a' & 'b'
• None of these

15. Equilibrium is a state in which:

• the forward reaction rate is more than the reverse reaction rate.
• the forward reaction rate is less than the reverse reaction rate.
• forward reaction rate and reverse reaction rate are equal. ✔
• forward reaction rate and reverse reaction rate become zero.

16. Conversion of ice into the water by melting and conversion of water into ice by freezing is an example of:

• chemical reaction
• reversible reaction ✔
• irreversible reaction
• None of them

17. A chemical reaction is a chemical change which involves:

• reactants
• products
• Both 'a' & 'b' ✔
• None of these

18. The direction of a reaction can be predicted by the type of arrow:

• doted lines
• single arrow ✔
• double arrow
• double straight line

19. A reversible reaction containing:

• one process
• two processes ✔
• three processes
• four processes

20. The reaction rate depends on the concentration of the:

• reactants ✔
• products
• temperature
• Both 'a' & 'b'

21. At the beginning the reaction:

• quantity of reactant is lower, and the rate of product formation is lower ✔
• quantity of reactant is lower, and the rate of product formation is higher
• quantity of reactant is higher, and the rate of product formation is lower
• quantity of reactant is higher, and the rate of product formation is higher

22. As the reactant amount decreases, the rate of reactant transformation:

• decreases ✔
• increases
• remains the same
• becomes zero

23. The state of dynamic equilibrium can be represented by:

• Rate of the forward reaction < Rate of the reverse reaction
• Rate of the forward reaction > Rate of the reverse reaction
• Rate of the forward reaction = Rate of the reverse reaction ✔
• Rate of the forward reaction - Rate of the reverse reaction = 0

24. In a reversible reaction, dynamic equilibrium is established:

• after the completion of reaction
• before the completion of reaction ✔
• it depends on the amount of reactants
• at any time

25. Which statement is TRUE for a forward reaction?

• It is always directed from right to left in a chemical reaction
• Product produces reactant
• Initially rate is fast but gradually slows down ✔
• All of them

26. Which statement is NOT true for reverse reaction?

• It is always directed from left to right in a chemical reaction ✔
• Product produce reactant (Reactants → Products)
• Initially rate is slow but gradually speeds up
• All of them

27. The rate at which a substance reacts is directly proportional to its:

• density
• concentration
• atomic mass
• active mass ✔

28. The rote of a reaction is directly proportional to the product of the active masses of the:

• products
• reacting substances ✔
• Both 'a' & 'b'
• None of them

29. Kc = :

• reactant x product
• ^reactant / _product
• ^product / _reactant ✔
• reactant = product

30. It is the single factor affecting the equilibrium constant's value.

• Density
• Pressure
• Temperature ✔
• Numbers of moles

31. Kc is independent of:

• reactant concentration
• Product concentration
• Both 'a' & 'b' ✔
• None of these

32. Kc varies with:

• temperature ✔
• reactant concentration
• product concentration
• densities

33. If Kc is larger than 1, the reaction is:

• in equilibrium
• reverse reaction
• forward reaction ✔
• None of them

34. The reaction is a reverse reaction, if Kc is:

• larger than 1
• less than 1 ✔
• equal to 1
• equal to 0

35. Which Statement is true if Q_c < K_c.

• increase in product concentration for equilibrium
• The forward reaction occurs, forming addition product
• Both 'a' & 'b' ✔
• None of these

36. If Q_c > K_c:

• There is increase in product concentration as the process reverses, forming more reactant.
• There is increase in product concentration as the process reverses, forming more product.
• There is decrease in product concentration as the process reverses, forming more product.
• There is decrease in product concentration as the process reverses, forming more reactant. ✔

37. If K_c is very small, then:

• reactions never finish ✔
• reactions are virtually complete
• reactions are Considered to be at equilibrium
• None of these

38. If K_c is very large, then:

• the concentration of reactants and products is almost same-
• the reaction has Maximum reactant concentration and minimum product concentration
• the reaction has maximum product concentration and minimum reactant concentration ✔
• None of them

39. This type of reaction is known as 'Forward reaction'.

• K_c is very small
• K_c is very large ✔
• K_c is neither very small nor very large
• K_c is equal to 0

40. These are the most important part of the atmosphere.

• oxygen & carbon dioxide
• nitrogen & oxygen ✔
• carbon dioxide & methane
• oxygen & ozone

FILL IN THE BLANKS:

1. Many physical and chemical changes are occurring in our surrounding which may be due to chemical reaction.
2. The chemical reactions may be reversible or irreversible.
3. The reversible reaction never goes to completion.
4. The state in which rate of forward reaction becomes equal to the rate of reverse reaction are known as equilibrium.
5. Chemical equilibrium always observed in reversible reactions.
6. In reversible reactions reactants and product inter convert into each other.
7. Reversible reactions proceed in either direction i,e forward and backward.
8. In dynamic equilibrium the rate of forward reaction is high, and rate of reverse reaction is slow in beginning.
9. Dynamic equilibrium can only be achieved in a closed container with fixed temperature.
10. According to law of mass action: "At any instant, the rate of a chemical reaction at a given temperature is directly proportional to the product of the active masses of the reactants at that instant."
11. K_c is equilibrium constant.
12. K_f is the rate constant for forward reaction.
13. K_r is the rate constant for reverse reaction.
14. An equilibrium constant K_c is used to show relationship between molar concentration of product and molar concentration of reactant.
15. As K_c is a ratio and usually has no unit.
16. K_c is independent of initial concentration of reactant and product.
17. K_c is temperature dependent.
18. The value of equilibrium constant, K_c tells us the extent of a reaction.
19. K_c also gives direction of reaction.
20. Q_c is known as reaction quotient.
21. Single headed arrow (→) used for irreversible reaction.
22. A double headed arrows (⇄) used for reversible reaction.
23. N_2(g) + 3H_2(g) → 2NH_3(g). is known as forward reaction or irreversible reaction.
24. N_2(g) + 3H_2(g) ← 2NH_3(g). is known as reversible reaction.
25. Equilibrium means a 'balance'.
26. Forward reaction is always directed from left to right in a chemical reaction.
27. Reverse reaction is always directed from right to left in a chemical reaction.
28. The concentration of reacting substance is called Active mass.
29. The unit of active mass is mol dm^-3.
30. The value of active mass is expresses in square brackets.
31. If K_c is larger than 1, the reaction is forward.
32. If K_c is less than 1, the reaction is reverse reaction.
33. Nitrogen and oxygen are 99% of the atmosphere and use to make chemicals.
34. Nitrogen of the atmosphere is used for preparation of ammonia.
35. Ammonia is used to prepare nitrogenous fertilizers.
36. Oxygen of the atmosphere is used for preparation of sulphur dioxide.
37. Sulphur dioxide is used to prepare sulphuric acid.

Elements With Symbols

• Cl ⇨Chlorine
• F ⇨ Flourine
• H ⇨ Hydrogen
• I ⇨ Iodine
• N ⇨ Nitrogen
• O ⇨ Oxygen
• S ⇨ Sulphur

Compounds With Formulas

• CO ⇨ Carbon monoxide
• CO₂ ⇨ Carbon dioxide
• COCl₂ ⇨ Carbonyl dichloride (Phosgene)
• HCl ⇨ Hydrochloric acid
• HI ⇨ Hydrogen iodide
• H₂O ⇨ Water
• H₂SO₄ ⇨ Sulphuric Acid
• Na₂CO₃ ⇨ Sodium carbonate
• NaHCO₃ ⇨ Sodium bicarbonate
• NH₃ ⇨ Ammonia
• NH₄Cl ⇨ Ammonium chloride
• NO ⇨ Nitric oxide
• NO₂ ⇨ Nitrogen dioxide
• SO₂ ⇨ Sulphur dioxide
• SO₃ ⇨ Sulphur trioxide

UNIT 04: CONTROL STRUCTURE - Question Answers - Computer Science For Class X (2021 and Onward)

GO TO INDEX

Computer Science For Class X
Unit 04: Control Structure
Question Answers

Q.1: What are control structures?
Ans. CONTROL STRUCTURE / STATEMENTS:
Control structures control the flow of execution in a program or function. Control structure are used to repeat any block of code, transfer control to specific block of code and make a choice by selection. There are three basic control structures in C++ progamming.

1. Selection / Decision making Control Structure
2. Loops / Iteration Control Structure
3. Jumps

Q.2: Define selection or decision making control structure and name its types.
Ans: SELECTION / DECISION MAKING CONTROL STRUCTURES / STATEMENTS:
The selection control structure allows a number of conditions which lead to a selection of one out of several alternatives. There are three types of selection control structure:

1. If selection structure/ statement
2. If-else selection structure/statement
3. Switch selection structure / statement

Q.3: Define if selection structure with syntax, flow diagram and example.
Ans: SELECTION STATEMENT:
An if statement is conditional statement that test a particular condition. Whenever that condition evaluates as true, performs an action, but if it is not true, then the action is skipped.

SYNTAX:

  The general syntax of if statement is:
 if (condition)
 {
 Statement (s);
 }

FLOW DIAGRAM

if SELECTION STATEMENT EXAMPLE

 #include<iostream>
 using namespace std;
 int main()
 {
 cout << "Enter an integer number:";
 cin >> num;
 if(num>0)
 cout << "You Entered a positive integer:" << num << "\n";
 }
 return0;
 }

OUTPUT

 Enter an integer number: 10
 You entered a positive integer: 10

Q.4: Define nested if selection structure with syntax and example.
Ans: NESTED if STATEMENT:
An if condition can be written as deeply as needed within the body of another statement. This is called nested if statement.

SYNTAX:

 The general syntax of nested if statement is:
 if (condition 1)
 {
 if (condition 2)
 {
 statement;
 }
 }

NESTED if STATEMENT EXAMPLE

  #include<iostream>
 using namespace std;
 int main()
 {
 int exp, status;
 cout << "Enter experience:";
 cin >> exp;
 cout << "\n Enter status:";
 cin >> status;
 if(exp>=4)
 {
 if(status>=2)
 cout << "\n Bonus Given to Employee" <<"\n";
 }
 }
 return0;
 }

OUTPUT

 Enter experience: 6
 Enter status: 3
 Bonus Given to Employee

Q.5: Define if-else selection structure with syntax, flow diagram and example.
Ans: if-else SELECTION STATEMENT:
An if-else selection structure performs certain action when the condition is true and some different action when the condition is false.

SYNTAX:

 The general syntax of if-else statement is:
 if (condition)
 {
 statement(s);
 }
 else
 {
 statement(s);
 }

FLOW DIAGRAM

if-else SELECTION STATEMENT EXAMPLE

 #include<iostream>
 using namespace std;
 int main()
 {
 int number;
 cout << "Enter an integer:";
 cin >> number;
 if(number>=0)
 {
 cout << "\n The number is a positive integer:" << number << "\n";
 }
 else
 {
 cout << "\n The number is a negative integer:" << number << "\n";
 }
 cout << "This line is always printed.";
 return0;
 }

OUTPUT

 Enter an integer: -5
 The number is a negative integer: -5
 This line is always printed.

Q.6: Define else-if selection structure with example.
Ans: else-if SELECTION STATEMENT:
Nested if-else statements test for multiple conditions by placing if-else statement inside if-else statements. When condition is evaluated as true, the corresponding statements are executed and rest of structure is skipped. This structure is also referred as the if-else-if ladder.

else-if SELECTION STATEMENT EXAMPLE

 #include<iostream>
 using namespace std;
 int main()
 {
 int per;
 cout << "Enter your percentage:";
 cin >> per;
 if(per>=80)
 {
 cout << "Your grade is A*:";
 }
 else if(per>=70)
 {
 cout << "Your grade is A:";
 }
 else if(per>=60)
 {
 cout << "Your grade is B:";
 }
 else if(per>=50)
 {
 cout << "Your grade is C:";
 }
 else
 {
 cout << "Failed.";
 return0;
 }

OUTPUT

 Enter your percentage: 70
 Your grade is A:

Q.6: Define switch statement with syntax, flow diagram and example.
Ans: SWITCH STATEMENT:
Switch statements is a control statements that allows to select only one choice among the many given choices. The expression in switch evaluates to return an integer or character value, which is then compared to the values present in different cases. It executes that block of codes which matches the case value. If there is no, match, then default block is executed (if present).

SYNTAX

 The general form of switch statements is,
 switch(variable)
 {
 case constant 1:
 {
 statement (s);
 break;
 }
 case constant 2:
 {
 statement (s); 
 break;
 }
 default:
 {
 statement (s);
 break;
 }
 }

FLOW DIAGRAM

SWITCH STATEMENT EXAMPLE

 #include<iostream>
 using namespace std;
 int main()
 {
 char op;
 float num1, num2;
 cout << "Enter an operator (+, -, *, /):";
 cin >> op;
 cout << "Enter two numbers: " <<"\n";
 cin >> num1 >> num2;
 switch(op)
 {
 case '+':
 cout << num1 <<"+" << num2 << "=" << num1 + num2;
 break;
 case '-':
 cout << num1 <<"-" << num2 << "=" << num1 - num2;
 break;
 case '*':
 cout << num1 <<"*" << num2 << "=" << num1 * num2;
 break;
 case '/':
 cout << num1 <<"/" << num2 << "=" << num1 / num2;
 break;
 default:
 cout << "Error! The operator is not correct";
 }
 return0;
 }

OUTPUT

 Enter an operator: +
 Enter two numbers:
 10 15
 10 + 15 = 25

Q.8: Write down the difference between if-else and switch statement.
Ans: DIFFERENCE BETWEEN if-else & SWITCH STATEMENT:

S.NO.	if-else	SWITCH
1.	if-else statement is used to select among two alternatives.	The switch statement is used to select among multiple alternatives.
2.	if-else statement can have values based on constraints.	Switch statement can have values based on user choice.
3.	Float, double, char, int and other data types can be used in if-else condition.	only int and char data types can be used in switch block.
4.	It is difficult to edit the if-else statement, if the nested if-else statement is used.	It is easy to edit switch cases as, they are recognized easily.

Q.9: What are loops or iteration and define its types?
Ans: LOOP / ITERATION CONTROL STRUCTURE:
Iteration or loop in computer programming, is a process wherein a set of instructions or structures are repeated in a sequence a specified, number of times until a condition is true. When the set of instructions is executed again, it is called an iteration. A loop statement allow us to execute a statement or a group of statements multiple times. C++ provides the following types of loops to handle looping requirements.

1. for loop
2. while loop
3. do-while loop

Q.10: Describe for loop with syntax, flow diagram and example.
Ans: for LOOP:
A for loop is a repetition or iteration control structure that repeats a statement or block of statement for a specified number of time. The for-loop statement includes the initialization of the counter, the condition, and the increment. The for loop is commonly used when the number of iteration is known.

SYNTAX
The general syntax of for loop is:

 for(initialization; test condition; increment/decrement)
 {
 statement(s);
 }

FLOW DIAGRAM

for LOOP EXAMPLE:

 #include<iostream>
 using namespace std;
 int main ()
 {
 int i;
 for(i = 1; <= 10; i++)
 {
 cout << i << "";
 }
 return0;
 }

OUTPUT

 1 2 3 4 5 6 7 8 9 10

Q.11: Describe while loop with syntax, flow diagram and example.
Ans: while LOOP:
The while loop allows the programmer to specy that an action is to be repeated while some conditions remain true. It is used when the exact numbert of loop repetitions befor the loop execution begins are not known.

SYNTAX

 The general syntax of while loop is:
 while(condition)
 {
 statement(s);
 }

FLOW DIAGRAM

while LOOP EXAMPLE:

 #include<iostream>
 using namespace std;
 int main ()
 {
 int i = 1;
 while(i <= 10)
 {
 cout << | << " ";
 i++, }
 return0;
 }

Q.12: Describe do while loop with syntax, flow diagram and example.
Ans: do while LOOP:
A do-while loop is similar to a while loop. except that a do-while loop is guaranteed to execute at least one time, even if the condition falls for the first time. Unlike for and while loops, which test the loop condition at the start of the loop, the do while loop checks its condition at the end of the loop.

SYNTAX

 The general syntax of a do-while loop is:
 while(condition)
 {
 do { statement(s);
 }
 while(condition);

FLOW DIAGRAM

do-while LOOP EXAMPLE:

 #include<iostream>
 using namespace std;
 int main ()
 {
 int i = 1;
 do {
 cout << i << " ";
 i++, }
 while (i <=10); return0;
 }

OUTPUT

 1 2 3 4 5 6 7 8 9 10

Q.13: Describe nested loop with example.
Ans: NESTED LOOP:
When one for, while or do-while loop is existed within another loop, they are said to be nested. The side loop is completely repeated for each repetition of the outside loop.

NESTED LOOP EXAMPLE:

 #include<iostream>
 using namespace std;
 int main ()
 {
 int row, column;
 for (row = 1; row <= 5; row++) {
 for (column = 1; column <= 3; column++) { cout << "+";
 cout << "\n";
 }
 return0;
 }

OUTPUT

+ + +
+ + +
+ + +
+ + +
+ + +

Q.14: Write down the differences between for, while and do-while loop.
Ans: DIFFERENCES BETWEEN for, while AND do-while LOOP:

S.NO.	for loop	while loop	do-while loop
1.	It is pre-test loop because condition is tested at the start of loop.	It is pre-test loop because condition is tested at the start of loop.	It is post-test loop because condition is tested at the end of loop which executes loop at least once.
2.	It is known as entry controlled loop.	It is known as entry controlled loop.	It is known as exit controlled loop.
3.	If the condition is not true first time then control will never enter in a loop.	If the condition is not true first time then control will never enter in a loop.	Even if the condition is not true for the first the control will never enter in a loop.
4.	There is no semicolon; after the condition in the syntax of the for loop.	There is no semicolon; after the condition in the syntax of the while loop.	There is a semicolon; after the condition in the syntax of the do-while loop.
5.	Initialization and updating is the port of the syntax.	Initialization and updating is not the part of the syntax.	Initialization and updating is not the part of the syntax.

Q.15: What re jumps statements.
Ans: Jump STATEMENTS:
These statements change the normal execution of program and jumps over the specific part of program.
Following are the jumps statements used in C++.

1. break
2. continue
3. goto
4. return
5. exit()

Q.16: Define break statement with example.
Ans: break STATEMENT:
The break statement allows you to exit a loop or a switch statement from any point within its body, bypassing its normal termination expression. It can be used within any C++ structure.

break EXAMPLE:

 #include<iostream>
 using namespace std;
 int main()
 {
 int count;
 for(count = 1; count <=100; count++)
 {
 cout << count;
 if(count = 10)
 break;
 }
 return0;
 }

Q.17: Define continue statement with example.
Ans: continue STATEMENT:
The continue statement is just the opposite of the break statement. Continue forces the next iteration of the loop to take place, skipping the remaining statements of its body.

continue EXAMPLE:

 #include<iostream>
 using namespace std;
 int main()
 {
 int count;
 for(count = 1; count <=10; count++)
 {
 if(count = 5)
 cout << count;
 }
 return0;
 }

Q.18: Define goto statement with Example.
Ans: goto STATEMENT:
In C++ programming, the goto statement is used for altering the normal sequence of program execution by transferring control to some other parts of the program.

goto EXAMPLE:

 #include<iostream>
 using namespace std;
 int main()
 {
 float num, average, sum = 0.0;
 int i, n;
 cout << "Maximum number of inputs:";
 cin >> n;
 for(i = 1; i<=n; i++)
 {
 cout << "Enter number" <<|<<":";
 cin >> num;
 if(num < 0.0)
 {
 // Control of the program move to jump:
 goto jump;
 }
 sum +=num;
 }
 Jump:
 average = sum / (n);
 cout << "\n Average = " << average;
 return0;
 }

Q.19: Define return statement with syntax.
Ans: return STATEMENT:
The return statement returns the flow of the execution to the function from where it is called. This statement does not mandatory need any conditional statements. As soon as the statement is executed the flow of the program stops immediately and return the control from where it was called.

STNTAX:

 return (expression / value);

Q.20: Define exit() statement with Syntax.
Ans: exit() STATEMENT:
The exit function, declared in <stdlib.h>, terminates a C++ program. The value supplied as as argument to exit is returned to the operating system as the program's return code or exit code.

SYNTAX:

 void exit (int);

Unit-5 - Respecting Self And Others - A Bad Dream - Text Book Exercise - Unit 5.2 - 5.6

Go To Index
Unit-5 - Respecting Self And Others
A Bad Dream
Text Book Exercise - Unit 5.2 - 5.6
English For Class X (2022 and Onward

By Mrs. Ayesha Arif
(Jauhar Progressive School)

UNIT 5.2
ORAL COMMUNICATION

UNIT 5.3
LANGUAGE PRACTISE
Revision of Number of Nouns

Nouns are either countable or uncountable. Those that are countable are either singular (one) or plural (more than one) in number.
Rules:

• Generally, the plural is formed by adding 's'.
  e.g.: chairs, days, flowers.
• Nouns ending in s, ch, sh, x usually take 'es'.
  e.g.: buses, churches, dishes, boxes.
• Nouns ending in 'y' change in two ways:
  * In nouns having a consonant before 'y', the 'y'  changes into 'ies'.
  e.g.: cherries, babies.
  * In nouns having a vowel before 'y' only 's' is added.
  e.g.: monkeys, keys.
• Nouns ending in 'o' can take 's' or 'es'.
  e.g.: radios. pianos, or mangoes, buffaloes.
• Nouns ending in 'f' or 'fe' change in two ways:
  * in some 'f' or fe' changes to 'ves':.
  e.g.: leaves, thieves, knives.
  * While some just take 's'.
  e.g.: beliefs, roofs, chiefs.
• Some are the same in singular and plural.
  e.g.: deer, sheep, hair.
• Some are used only in the plural.
  e.g.: police, scissors, scales, trousers, jeans, spectacles.
• In some cases, there is no fixed rule.
  e.g.: children, oxen, teeth, feet, men, women, mice.
• In most compound nouns 's' is added at the end.
  e.g.: check-ups, doorbells, stepfathers.
• In some compound nouns the 's' is added to the first part.
  e.g: brothers-in-law.

EXERCISE 1

Form plurals of the following singular nouns. After completing, compare your answers with your partner.

S.NO.	Singular Noun	Plural Noun
1.	Story	Stories
2.	Hair	Hairs / Hair
3.	Child	Children
4.	Leaf	Leaves
5.	Son in Law	Sons in law
6.	Tooth	Teeth
7.	Woman	Women
8.	Thief	Thieves
9.	Port folio	Port folios
10.	Studio	studios
11.	Secretary of state	Sectaries of state
12.	News	News
13.	Hoof	Hoofs
14.	Theory	Theories
15.	Trousers	Trousers
16.	Hair	Hairs / Hair
17.	Essay	Essays
18.	Valley	Valleys
19.	Tooth	Teeth
20	Chimney	Chimneys

EXERCISE 2

Fill in the blanks with appropriate plural forms of the given nouns. After completing, compare your answers with your partner.
1. I saw three big oxen (ox) near the cliffs (cliff).
2. There were many police (police) near those houses (house).
3. Please buy some potatoes (potato) and tomatoes (tomato).
4. Farmer Abdul Raheem has three sheep (sheep) and four deer (deer) on his farm.
5. Mrs. Jahanzaib had to go for check-ups (check up) every week.
6. Raja is more than six feet (foot) tall, but he is afraid of mice (mouse).
7. The little calves (calf) lost their mothers (mother).
8. There are three banks (bank)in the four cities (city) close to my village.
9. We need more knives (knife) and forks (fork).
10. My sister has lost three of her teeth (tooth).

EXERCISE 3

Work in pairs. Write down the plural of the given nouns. Then, form sentences using both the singular and plural nouns in your own sentences. An example is given below.
Example:

• Radio: My grandfather has one very old radio.
• Radios: There are several types of radios in this shop.

S.NO.	Word	Sentence
1.	Leaf	The teacher brought a long leaf for the practical.
	Leaves	The trees shed their leaves in autumn season.
2.	Dish	He told his mother to pass the dish of mutton.
	Dishes	The girl was washing the dishes in the kitchen.
3.	Father in law	His father in law is a doctor.
	Fathers in law	The grooms ususally do not their fathers in law just like.
4.	Train	The train left the station on exact time.
	Trains	Several trains were late due to the accident on railway track.
5.	Boy	The boy is learning to operate computer.
	Boys	Boys are always interested in vehicles.
6.	Witch	The witch casts her spell on the girl.
	Witches	There are three witches in the novel Macbeth.
7.	Thief	The thief stole her precious jewellery.
	Thieves	The thieves stole everything from the jewellery shop.
8.	Donkey	The farmer had a lazy donkey.
	Donkeys	Donkeys are often called beasts of burdens.
9.	Hair	The baby had a nice hair cut.
	hairs	The girls keep their hairs clean.
10.	Child	The nurse took the child to the nursery.
	Children	The children are playing happily in the ground.

Modal Verbs (request and advice)

Modal Verbs for Formal and Informal Requests
Formal Request
May, Would, and Could are used in formal, polite requests.

• May I borrow your pen, please?
• Could you help me for a minute, please?
• Would you explain that again, please? I didn't understand?

Informal Request
Will and can are used in informal, casual requests.

• Will you please answer the phone? I'm working.
• Can you hold my books for me? My hands are full.

EXERCISE 4

Work in pairs. Orally discuss and change the following statements into requests by using modal verbs. After discussing, write the requests sentences in your note book.
1. Shut the door, as it is windy today.
Would you please Shut the door, as it is windy today.

2. Send me an email and I'll follow it up.
Would you please Send me an email and I'll follow it up.

3. Help me finish this assignment.
Will you please Help me finish this assignment.

4. Pass the salt and pepper.
Can you please Pass the salt and pepper.

5. Repeat what you just said.
Could you please Repeat what you just said.

6. Help me find my leather jacket.
Can you please Help me find my leather jacket.

7. Clear the table so that I can put my computer there.
Will you please Clear the table so that I can put my computer there.

8. Show me how to do fix this problem.
Could you please Show me how to do fix this problem.

9. Help her in whatever way you can.
Would you please Help her in whatever way you can.

10. Move this chair in the corner.
Could you please Move this chair in the corner.

Advice

The modal verbs for advice are should, ought to, and had better. These can be used in positive and negative sentences.
For example:

Positive Sentence	Negative Sentence	Interrogative Sentence
You should study harder to get better results.	You shouldn't call her while she is busy with chores.	I have a problem. Should I call my parents or my friend?
You ought to wear a warm jacket, it's really cold outside.	("ought to" is not usually used in the negative form)	("ought to" is not common in question form)
You had better slow down. You are driving too fast!	You had better not forget to finish your) homework.	("had better is not usually used in question form)

The phrase "had better" is a bit stronger. It includes the idea of a warning: something terrible will happen if you do not follow my advice.

EXERCISE 5

Work in pairs. Orally discuss and change the following statements into advice by using modal verbs. After discussing, write the advice sentences in your notebooks.
1. Listen to your mother.
Ans: You should listen to your mother.

2. Give good reason for your absence.
Ans: You ought to give good reason for your absence.

3. Break traffic rules.
Ans: You had better not Break traffic rules.

4. Fulfill the promise you made to your mother.
Ans: You should fulfill the promise you made to your mother.

5. Finish your task on time or you'll be in trouble.
Ans: You had better Finish your task on time or you'll be in trouble.

6. Discuss this matter on the dinner table.
Ans: You should Discuss this matter on the dinner table.

7. Remain seated until the seatbelt sign is turned off.
Ans: You ought to Remain seated until the seat belt sign is turned off.

8. Complete these chores by tomorrow.
Ans: You should complete these chores by tomorrow.

9. Talk when others are speaking.
Ans: You had better not Talk when others are speaking.

10. Follow the instructions carefully.
Ans: You ought to Follow the instructions carefully.

EXERCISE 6

Write requests or advice for the following situations.
a) You need a pen, and your sister has one.
Ans: May I take your pen please?

b) You are spending too much money on buying unnecessary clothes.
Ans: You had better not spend money on buying unnecessary clothes.

c) Your friend is leading an unhealthy lifestyle.
Ans: You should take care of your health.

d) You want a half-day leave from your Principal as there is an emergency in your family.
Ans: would you please grant me half day leave as I have an urgent piece of work at my home?

e) Your brother is going to the stadium to watch a cricket match and you want to go with him.
Ans: Can I go with you to the stadium to watch the cricket match?

f) My friend was telling me a secret about her family.
Ans: You should not tell me a secret about your family.

g) What does your mother say if you spend too much time playing games rather than studying?
Ans: You had better to give time to your study rather playing games.

h) The phone rings while you are cooking in the kitchen. Your father is near the telephone.
Ans: Can you please attend the call Dad?

i) It's hot, and you are thirsty.
Ans: Could you please give me a glass of water, I am so thirsty?

j) You're studying for an exam, but your brother listens to loud music.
Ans: Can you please turn the music down brother, I am studying?