Pakistan Studies - Years And Important Incidents (مطالعہ پاکستان - سن اور اہم واقعات)

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Chapter -13 - Shahariyon K Haqooq Ka Tahafooz Aur Idaaro Ka Kirdaar - Pakistan Studies (مطالعہ پاکستان - دہم کلاس کے لۓ) - Fill In The Blanks And Multiple Choice Questions (MCQs)

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Chemistry For Class IX (New Book ) - Chapter No. 2- Atomic Structure - Detailed Questions And Answers

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Chapter No.2-Atomic Structure
Detailed Questions And Answers

Q.1: Define Atom? Also describe the discovery of Sub Atomic Particles ( electron, proton and neutron) of an atom.
Ans: ATOM:
Definition:
By Democritus
The word atom is derived from a Greek word 'ATOMOS' means indivisible, which was first describe by Greek philosopher Democritus. Democritus belief that:

"All matter consist of very small indivisible particles which are known as atoms."

By Johan Dalton:
Johan Dalton an English school teacher and chemist suggested the fundamental atomic theory, which explain that:

"All element are made up of indivisible particles called atoms."

Discovery of Sub Atomic (Electron, Proton, Neutron) Particles Of An Atom:
Dalton assumed that no particles smaller then atom exit. Dalton’s atomic theory explains the chemical nature of matter and existence of indivisible atoms, but at the end of 19^th century sub-atomic particles were discovered by different scientists. New experiments show that:
"Atom is composed of even smaller particles which are known as sub-atomic particles.
After that these sub-atomic particles were discovered and named as electron, proton and neutrons.

1. Electron: First sub-atomic particle Electron discovered by M. Farady, William Crooks and J.J. Thomson.
2. Proton: Second sub-atomic particle Proton identified by Goldstein and Ernest Rutherford.
3. Neutron: Third sub-atomic particle Neutron revealed by Chadwick.

All of these findings were milestone in the knowledge of atomic structure which we have now.

Q.2: Describe the Thomson's experiment or discharge tube experiment for the discovery of electrons? Also write down the properties of cathode rays?
Ans: Discovery Of Electron:
Electron is the lightest particle carrying negative charge in an atom discovered by J.J.Thomson and William crooks.

Thomson's Experiment Or Discharge Tube Experiment:
In 1897 J. J. Thomson carried out an experiment for the discovery of an electron.
Discharge Tube:
The apparatus used for this type of experiment is called discharge tube which consists of glass tube fitted with two metal electrodes connected to a high voltage source and a vacuum pump.
Working:
When electrodes inside evacuated, discharge tube are connected with high voltage source at very low pressure (1 mm of Hg), as the high voltage current start passing between electrodes a streak of bluish light originate and travel in straight line from cathode (-ve electrode) to anode (+ve electrode), Which cause glow at the wall of opposite end. These rays ere called cathode rays.
Conclusion:

• J.J.Thomson justified that these rays were deflected towards positive plate in electric and magnetic field which shows that these rays possess negative charge due to this negative charge, particle was named Electron.
• These electrons were obtained from the gas in discharge tube which proves that electrons are constituent of all matter.

Properties of Cathode Rays (Electrons):

1. They travel in straight line from cathode towards Anode.
2. They produce sharp shadow of an opaque object placed in their path.
3. They have negative charge and bend towards positive plate in electric and magnetic field.
4. These rays when strike with glass and other material cause material glow.
5. The (e/m) charge and mass ratio of cathode particles is 1.7588 x 10⁸ coulomb per gram. This is same for all electrons, regardless of any gas in discharge tube.
6. They can produce mechanical pressure indicating they possess kinetic energy (K.E).

Q.3: Describe the discovery of proton? Also write down the properties of canal rays?
Ans: Discovery of Protons
The Proton is positively charge particle discovered by Goldstein in 1886. J. J.Thomson investigate properties of proton in 1897.
Discharge Tube:
Protons were observed in same apparatus of cathode rays tube but with perforated cathode.
Working:
Goldstein discovered that not only negatively charge cathode rays but positively charge rays are moving in opposite direction by perforating cathode. These positive rays passes through the holes of cathode, where they strike cause the glow of tube. These rays named as Canal rays (proton).
The canal rays are not emitted by anode, but they are result of striking of electron with residual gas molecules in discharge tube. Electrons ionize the gas molecules as follows.

M + e^- ⟶ M⁺¹ + 2 e^-

Conclusion:
Goldstein justify that atoms are electrically neutral, while electrons carry negative charge. It mean for each electron there must be one equivalent positive charge to neutralize that electron. This particle is called proton and it is a fundamental particle of all Atoms.

Properties of Canal Rays (Protons):

1. They travel in straight line from Anode towards Cathode.
2. They produce sharp shadow of object placed in their path.
3. They have positive charge and bend towards negative plate in electric and magnetic field.
4. The (e/m) charge and mass ratio of positive particles is much smaller than electron. It varies according to nature of gas present in tube.
5. The mass of proton is 1836 times more than electron.

Q.4: Describe the discovery of neutron? Also write down the properties of neutrons?
Ans: Discovery of Neutrons:
In 1920 Rutherford predict that atom must possess another neutral particle with equivalent mass of proton. Different scientists started working on this neutral particle. later on 1932 Chadwick become successful to discover Neutron.
Experiment:
Chadwick found that when alpha (μ)particles bombarded on Beryllium some penetrating radiations were given out. Chadwick suggested that these radiations were due to material particle with mass comparable to hydrogen atom but have no charge. These radiations (particle) are called Neutron. It can expressed in equation as follows.

⁹₄Be + ⁴₂He ⟶ ¹²₆C + ₀n¹

Conclusion:
The neutron is fundamental part of an Atom, present in nucleus with proton and include in atomic mass.

Properties of Neutrons:

1. The Neutrons are neutral particles.
2. They have no charge.
3. The mass of neutron is almost equal to that of proton.
4. These particles are most penetrating in matter.

Q.5: How Atomic Number (Z) and Mass Number (A) are related with number of proton and neutron?
Ans: Atom consist of three particles Electron, Proton and Neutron. But if all atoms have same fundamental particles, then none of the atoms of one element can be different from the atoms of another element. Therefore, all atoms can be identified by their atomic number i.e the number of protons they contain. No two elements have the same number of protons. In neutral atoms number of protons are equal to number of electrons.
While the total number (sum) of proton and neutrons in the nucleus of an atom is called Mass Number.
For example:
Atom of Carbon (C) is different from an atom of Nitrogen, because atomic number of carbon is 6 while the atomic number on nitrogen is 7, and the mass number of of carbon is 12 while the atomic number on nitrogen is 14.

Q.6: Define Atomic Number (Z) and Mass Number (A) in term of number of proton and/or neutron?
Ans: Atomic Number (Z):

"The number of protons in the nucleus of an atom is called Atomic Number."

Atomic number is represented by Z.
The elements are identify by their atomic number. Different elements have different atomic numbers because of different number of protons.
In neutral atoms number of protons are equal to number of electrons, so the atomic number also indicate total number of electrons outside the nucleus.
For example:
Atomic number of Carbon(C) is 6. It mean that each carbon atom has 6 protons and 6 electrons in it.
Formula:
Atomic number= Z = Number of proton in nucleus = Total number of electron around nucleus
Atomic number (Z) is written as subscript on the left hand side of the chemical symbol.
e.g

• Carbon: C₆
• Lithium: Li₃
• Oxygen: O₈
• Hydrogen: H₁ etc.

Mass Number (A):

"The total sum of proton and neutrons in the nucleus of an atom is called Mass Number."

Mass number is represented by A.
For example:
The sodium (Na) atom has atomic number 11 and mass number 23. It indicates that sodium atom has 11 protons and 12 neutrons. The mass number (A) is written as superscript on left hand side of chemical symbol.
e.g
²³₁₁Na
Formula:

• Mass number = A = Number of protons (Z) + Number of neutrons (N) OR
  Mass number A = Z + N
• Number of neutron = Mass number - Atomic Number. OR
  Number of neutron N = A – Z

Q.7: Describe the contributions Rutherford made to the development of the atomic theory.

OR

Describe Rutherford's experiment which led him to the discovery of the electron.
Ans: Rutherford Atomic Model
EXPERIMENT:
Gold Foil experiment
Rutherford took a thin sheet of gold and bombarded it with alpha (α) particles obtained from a radioactive element (Like Polonium). These rays scattered from the atom and examined on a zinc sulphide (ZnS) screen.

Observations:

1. Most of the particles passed straight and undeflected through the sheet and produced illumination on the zinc sulphide screen.
2. Very few alpha (α) particles undergo small and strong deflection after passing through gold sheet.
3. A very few alpha (α) particles (one of 8000) retraced their path.

Conclusion:

1. According to Rutherford an atom consist of two parts nucleus and extra nuclear part.
2. Majority of the alpha particles passed straight line and un-deflected, shows that most volume occupied by atom is empty.
3. Alpha particles are positively charged and their deflection indicates that the spelling of atom has a positive charge, which is named as nucleus.
4. The mass is concentrated in the nucleus and the electrons are distributed outside the positively charge nucleus.
5. The electrons are revolving around the nucleus in extra nuclear part in orbits.

Q.8: Write down the postulates Rutherford's atomic model? Also describe the drawbacks of Rutherford's atomic model?
Ans: Rutherford postulates:

1. An atom consist of positively charged, dense and very small nucleus containing protons and neutron. The entire mass is concentrated in the nucleus of an atom.
2. The nucleus is surrounded by large empty space which is called extra nuclear part where probability of finding electron is maximum.
3. The electrons are revolving around the nucleus in circular paths with high speed (Velocity).
4. These circular paths were known as orbits (Shells).
5. An atom is electrically neutral because it has equal number of protons and electrons.
6. The size of the nucleus is very small as compared to the size of its original atom.

Defects of Rutherford atomic model:

1. Rutherford did not explain the stability of an atom.
2. In Rutherford atomic model the negatively charged electrons revolve around the nucleus in circular path and emits energy continuously. Due to continuous loss of energy ultimately falls into the nucleus.
3. If the revolving electron continuous emits energy, then there would be a continuous spectrum but in contrast to it we get line spectrum from the atoms of elements.

Q.9: Explain how Bohr's atomic model is different? Write down salient features or postulates of Neil Bohr's atomic model?
Ans: Neil Bohr’s Atomic model:
In 1913 Neil Bohr proposed another atomic model. This atomic model was different in this manner that it shows two folds:

1. First to remove the Rutherford atomic model.
2. Second, it explain the line spectrum of Hydrogen atom based on quantum theory of Max Planck.

Postulates of Neil Bohr's Atomic Model:
Neil Bohr proposed the following postulates for atomic structure.

1.  The atom has fixed orbits in which negatively charged electron is revolving around the positively charged nucleus.
2. These orbits possess certain amount of energy which are called shells and named as K, L, M, N shells.
3. The energy levels are represented by an integer (n = 1, 2, 3….) known as quantum number, this quantum range starts from nucleus side, where n = 1 is lowest energy level.
4. Electrons are revolving in particular orbits continuously, but they are not emits or absorb energy.
5. When electron jumps from lower energy level (E₁) to higher energy level (E₂), it absorb energy.
6. When electrons jumps from higher energy level (E₂) to lower energy level (E₁), it emits energy.
7. The emission or absorption is discontinuous in the form of energy packet called Quantum or Photon.
8. The ΔE is the difference in energy of higher (E₁) and lower (E₂) energy level.
   
   ΔE =E₂ – E₁
   ΔE = νh = 1 photon
   Here h is planks constant, its value is 6.63 x 10^-34 Js and ν is a frequency of light.
9. Stationary state were present in those orbits in which angular moment of electron would be integral multiple of h/2pπ.
   
   mνr = nh / 2pπ
   where,
   n = no of orbits
   h = planks constant
   m = mass of electron

Q.10: Write down the limitation or the drawbacks of Bohr's atomic model?
Ans: Limitations Or Drawback of Bohr's Atomic Model:

• Bohr's model of an atom failed to explain the Zeeman Effect (effect of magnetic field on the spectra of atoms).
• It also failed to explain the Stark effect (effect of electric field on the spectra of atoms).
• It deviates the Heisenberg Uncertainty Principle.
• It could not explain the spectra obtained from larger atoms.
• It explain the monoelectronic species like H⁺¹, Li⁺², B⁺³.

Q.11: Describe De Broglie Hypothesis atomic model? OR Describe wave particle duality of electron of De Broglie Hypothesis?
Ans: De Broglie Hypothesis:
In 1923 Lois De Broglie extend the wave particle duality to electron, and propose a hypothesis that:

"All matter has particle as well as wave nature at the submicroscopic level."

De Broglie combine the Einstein and Planck equations and argued that if

E = hγ (Plank equation) ....... (i)

where,
E = energy,
h = plank 'constant,
γ = frequency of light

And

E = mc² (Einstein equation) ....... (ii)

where,
E = energy,
m = mass,
c = speed of light

Then From eq. (i) and (ii)

hγ = mc²

OR γ= mc²/h ......... (iii)

According to De-Broglie wave particles duality hypothesis

λ = h /mγ ..... (iv)

The wave nature of a particle is quantified by De Broglie wavelength defined as:

λ=h/p

where
p is the momentum of the particle.
So,
According to De-Broglie

"A light, or any other electromagnetic wave, can also exhibit the properties of a particle, similarly a particle should also exhibit the properties of a wave, and those two nature are interchangeable."

Q.12: Describe Schrodinger atomic model?
Ans: Schrodinger Atomic Model hypothesis
In 1926 Erwin Schrödinger, an Austrian physicist, took the Bohr’s atomic model one step forward. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom.
Schrodinger model is just an improvement of Bohr’s atomic model. He took an atom of hydrogen because it has one proton and one electron. He proved mathematically that electron can be find in different position around the nucleus and determined by probability.

Postulates Of Schrodinger Atomic Model

• The quantum mechanical model determines that electron can be find in various location around the nucleus. He found electrons are in orbit as an electron cloud.
• Each energy sub-shell in an orbit have different shapes which determine the presence of electron.
• Different sub-shells of orbitals are orbitals named as s, p, d and f with different shapes as 's' is spherical and 'p' is dumbbell shaped.
• The numbers and kind of atomic orbitals depends on the energy sub-shell.

Probability:

• According to quantum mechanical model probability of finding an electron within certain volume of space surrounding the nucleus can be represented as a fuzzy cloud.
• The cloud is denser the probability of finding electron is high which are called atomic orbitals.

Q.13: Describe shells Or orbits Or energy level of an atom?
Ans: ENERGY LEVELS OR ORBITS OR SHELLS OF AN ATOM:
Nucleus is present in the centre of an atom and around the nucleus electrons are revolving. These electrons are revolving around nucleus in different levels according to their potential energy.
Definition:

"The Energy levels or Shell or Orbit are all possible paths on which electrons are revolving around nucleus."

Which are shown by 'n'.
These shells are named as K, L, M, N, O, P with quantum numbers n = 1, 2, 3, 4, 5, 6 respectively.

Order Of Energy In Shells:
These shells have definite amount of energy by means of decreasing order as they become away from nucleus. Such as:

• First energy level is K shell has less energy.
• Second energy level is L shell has more energy than K shell.
• Third energy level is M shell has more energy than K and L shells.
• Fourth energy level is N shell has more energy than K, L and M shells.
• Fifth energy level is O shell has more energy than K, L, M and N shells.

Number of Electrons In Shells:
Formula:
The maximum number of electrons that can be accommodated in a shell is represented by the formula:

2n²

where 'n' is the shell number.
The distribution of electrons in different orbits are as follows:

• K-shell/ 1^st orbit (n = 1) = 2(1)² = 2
• L-shell/ 2^nd orbit (n = 2) = 2(2)² = 8
• M-shell/ 3^rd orbit (n = 3) = 2(3)² =18
• N-shell/ 4^th orbit (n = 4) = 2(4)² = 32 and so on

Q.14: Describe sub shells Or sub energy level Or orbitals? OR Describe the presence of sub shells in a shell.
Ans: SUB SHELLS OR SUB ENERGY LEVELS Or ORBITALS:
When atomic spectra of substances were observed in a high powered spectroscope, it was found that they consist of two or more lines closely packed with each other as discussed in zemen and stark effects. These lines means that electrons in the same shell may differ in energy by small amount. Thus:
Definition:

"Main energy level are divided into sub energy levels and known as sub shells. When electrons are many in numbers in a shell they show repulsion and main shell splits into sub shell which named as s, p, d and f sub shells."

Number Of Sub Shells In Shells
The number of subshells in a shell is according to value of that shell, which are as follows:

Value of ‘n’	Shell	Sub shell
1	K	s
2	L	s, p
3	M	s, p, d
4	N	s, p, d, f

Number Of Electron In Sub Shells:
There are slight difference in Energy levels of subshells, that way subshell 's' filled first then subshell 'p' and onward. The distribution of maximum electrons in subshells is as follows:

• 2 electrons in's' subshell
• 6 electrons in 'p' subshell
• 10 electrons in 'd' subshell
• 14 electrons in 'f' subshell

SECTION- C:  QUESTIONS:

Chapter -1 - Pakistan KI Nazriyati Ahsaas - Pakistan Studies (مطالعہ پاکستان - دہم کلاس کے لۓ) - Short Question Answer

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باب 01 - پاکستان کی نظریاتی اساس
مختصر سوال جواب

Chapter -1 - Pakistan KI Nazriyati Ahsaas - Pakistan Studies (مطالعہ پاکستان - دہم کلاس کے لۓ) - Detailed Question Answer

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باب 01 - پاکستان کی نظریاتی اساس
تفصیلی سوال جواب

Chapter -1 - Pakistan KI Nazriyati Ahsaas - Pakistan Studies (مطالعہ پاکستان - دہم کلاس کے لۓ) - Fill In The Blanks And Multiple Choice Questions (MCQs)

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باب 01 - پاکستان کی نظریاتی اساس
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Properties of Matter - Physics For Class IX (Science Group) - Numericals

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Physics For Class IX (Science Group)
UNIT 7: PROPERTIES OF MATTER
Numericals

WORKED EXAMPLES

Numerical From Text Book Exercise

Gases and Kinetic theory
7. The pressure on 9 cm³ of oxygen gas is doubled at a fixed temperature. What will its volume become?
Solution:
Data:

• Initial pressure = P₁ = P₁
• Final pressure = P₂ = 2P₁
• Initial volume = V₁ = 9 cm³
• Final Volume = V₂ = ?

Working Formula:

P₁V₁ = P₂V₂

Calculation:

P₁ x (9) = (2P₁) x V₂

Ans: Hence, Its volume will become 4.5 cm³

8. A container holds 30 m³ of air at a pressure of 150000 Pa. If the volume changed to 10 m³ by decreasing load on the piston. What will the pressure of the gas become? Assume that its temperature remains constant.
Solution:
Data:

• Initial pressure = P₁ = 150000 Pa
• Final pressure = P₂ = ?
• Initial volume = V₁ = 30 m³
• Final Volume = V₂ = 10 m³

Working Formula:

P₁V₁ = P₂V₂

Calculation:

(150000) x (30) = P₂ x (10)

4500000 = P₂ x (10)

P₂ = ^4500000/₁₀ = 450000 pa.

Ans: Hence, The pressure of the gas will become 450000 pa

9. Air at atmospheric pressure of 760 mm of Hg is trapped inside a container available with a moveable piston. When the piston is pulled out slowly so that the volume is increased from 100 dm³ to 150 dm³, the temperature remaining constant. What will be the pressure of the air becomes?
Solution:
Data:

• Initial pressure = P₁ = 760 mm of Hg
• Final pressure = P₂ = ?
• Initial volume = V₁ = 100 dm³
• Final Volume = V₂ = 150 dm³

Working Formula:

P₁V₁ = P₂V₂

Calculation:

(760) x (100) = P₂ x (150)

76000 = P₂ x (150)

P₂ = ⁷⁶⁰⁰⁰/₁₅₀ = 506.67 mm of Hg

Ans: Hence, The pressure of the air will become 506.66 mm of Hg

Properties of Matter - Physics For Class IX (Science Group) - Self Assessment Questions and Test book Exercise

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Physics For Class IX (Science Group)
UNIT 7: PROPERTIES OF MATTER
Self Assessment Questions and Test book Exercise

SELF ASSESSMENT QUESTIONS:

Q.1: Explain why the measurement of volume of a given liquid remains same although it is measured by measuring cylinders of different shapes and sizes.
Ans: The measurement of volume of a given liquid remains same, because, the forces of attraction between particles are strong and the particles are free to move about within the liquid. Due to these features liquids have fixed volumes, but they take the shape of the container, so it is measured by measuring cylinders of different shapes and sizes.

Q.2: What is the difference between evaporation and boiling?
Ans: Difference Between Evaporation and Boiling

S.NO.	Evaporation	Boiling
1.	Evaporation can occur at any temperature.	Boiling always occurs at a fixed temperature.
2.	In this process, no bubbles are formed.	Bubbles are formed as a result of air enters inside the liquid.
3.	It takes place only on.the surface of the liquid.	It takes place throughout the liquid.
4.	The temperature of the liquid body decreases when evaporation takes place.	In contrast, the temperature remains constant in this process.
5.	Evaporation continues as long as the air above the surface of liquid remains unsaturated.	It takes place until the internal temperature of the liquid is equal to the external temperature of the surroundings.
6.	Sunlight or surrounding temperature is the major source to initialize evaporation.	To initialize this process, a heat energy source is supplied to the liquid.

Q.3: What is the difference between three states of matter? in terms of the spacing between the molecules.
Ans: Difference Between Three states Of Matter (solids, Liquids And Gases):

S.NO	SOLIDS	LIQUIDS	GASES
1.	The molecules are closely packed together and occupy minimum space.	The molecules are slightly further apart compared to that of solids.	The molecules are very far apart.
2.	The molecules usually arranged in a regular pattern called lattice.	The molecules occur in clusters.	The molecules are arranged randomly.
3.	Molecules can not move.	Molecules can move about, and slide past each other.	Molecules are free to move with very high speeds.
4.	There is a large number of particles per unit volume. That is why solids have the highest densities.	There is slightly less number of particles per unit volume compared to solids.	There is small number of particles per unit volume. Gases have low density

Q.4: Why Tungsten melts at a much higher temperature than iron?
Ans: Tungsten melts at a much higher temperature than iron because of its heaviness and covalent bond between the atoms. It is well known that elements with a higher atomic mass have higher melting points. For Tungsten there is the added indication that some of its valence electrons (the 5d electrons) are making covalent bonds between neighbouring atoms in the crystal structure. In general, the greater the number of valence electrons, the stronger is the resultant bonding. Tungsten has the maximum number of unpaired electrons and therefore, it is one of the very hard metals and has maximum enthalpies of atomization. So tungsten has a very melting point.

Q.5: What is the name of process in which a liquid changes into a solid?
Ans: Freezing is a phase transition in which a liquid turns into a solid when its temperature is lowered to its freezing point.

Q.6: What is the name of temperature at which a liquid changes into a solid?
Ans: The name of temperature at which a liquid changes into a solid is the freezing point. It is the temperature at which a liquid becomes a solid at normal atmospheric pressure.

Q.7: Draw diagrams of the molecules in a gas to explain the effect of pressure change on its volume.

Q.8: What is the meant by the subscripts 1 and 2 in the equation, p₁V₁ = p₂V₂?
Ans: In above equation of Boyle's law,

• The subscript '1' means 'initial' pressure and volume and
• The subscript '2' means 'final' pressure and volume.

Q.9: What is the effect of temperature on average translational kinetic energy of molecules?
Ans: TEMPERATURE:
The temperature of a gas is determined by the average translational kinetic energy of its molecules. If a gas is heated the average translational kinetic energy of its molecules increases and temperature of the gas rises. If a gas is cooled down the average translational kinetic energy of its molecules decreases and temperature of the gas falls.

Test book Exercise

Section (B) Structured Questions
Kinetic molecular model of matter
1.a) “The particles are free to move within the material, has a fixed volume but takes up the shape of its container”, which state of matter is being described here?
Ans: Liquids.

1.b) Write a similar description of the particles that make up a solid.
Ans: The particles are closely packed together and usually arranged in a regular pattern called a lattice. The forces of attraction between particles are very strong. The particles are not able to change position. Therefore, solids have fixed shapes and volumes.

1.c) Write down any two properties of a solid.
Ans: Properties Of Solids:

• The particles in solids have following features:
• The molecules are closely packed together and occupy minimum space.
• The molecules usually arranged in a regular pattern called lattice.
• There is a large number of particles per unit volume. That is why solids have the highest densities.
• The movement of particles in solids have following features:
• The forces of attraction between particles are very strong.
• The particles are not able to change positions.
• The particles vibrate about fixed positions thus are not entirely stationary.
• This explains why solids have fixed shapes and volumes.

(Note: Write down any two properties as mention in quesation)

2.a) Why the kinetic model of matter is called kinetic?
Ans: Any matter that is moving has energy just because it's moving. The energy of moving matter is called kinetic energy. Scientists think that the particles of all matter are in constant motion. In other words, the particles of matter have kinetic energy. The theory that all matter consists of constantly moving particles is called the kinetic theory of matter or Kinetic model of matter.

2.b) In which state of matter the molecules are widely separated?
Ans: Gas.

2.c) In which state of matter the molecules are most closely packed?
Ans: Solid.

2.d) In which state of matter molecules can move freely at high speed?
Ans: Gas.

3.a) By using kinetic molecular theory explain why we can walk through air, swim through water but can not walk through a solid wall.
Ans: According to kinetic molecular theory, there is not a little space between the particles of solids as compared to liquids and gases. The forces of attraction between these particles are so strong that we cannot pass through solid objects, such as walls.

3.b) In which state of matter do the molecules have minimum kinetic energy?
Ans: Solids.

3.c) Which state of matter is highly incompressible?
Ans: Solids.

Forces and Kinetic Theory
4. A sample of a gas is in a sealed test tube is cooled. Describe what happens to:
a) The size of the molecules.
Ans: No effect.

b) The speed at which molecules move.
Ans: Decrease.

c) The number of the molecules.
Ans: Remains the same.

d) The pressure inside the tube.
Ans: Decrease.

e) The state of the gas.
Ans: At a very low temperature, it will change into liquid.

5. An inflated car tyre is considered to have a constant volume, regardless of any changes in temperature or pressure. Use the kinetic molecular theory of gases to answer the following:
a) How does air in the tyre exert a pressure on the walls of the tyre?
Ans: A tyre of a car exert force on the road against the friction between the road and the surface of the car, while the car is moving on road. As a result air (gas) molecules in the tyre collide with the tyre wall and produce force with energy. Gas pressure is caused when gas particles hit the walls of their container. The more often the particles hit the walls, the faster the tires are moving on the road, the higher will be the pressure. The increased speed of the molecules will increase the number of collisions per second with the tyre wall. This in turn results in an increased force and therefore increased pressure on the tyre wall.

Also the moving car has to do work against the friction. This work results in the transfer of energy to the tyres as heat.
According to pressure law, "For a fixed mass at constant volume, the pressure is directly proportional to the temperature (In Kelvin)." Hence the increase in temperature will result in increase in pressure.

b) Why is the pressure the same at all points on the inside wall of the tyre?
Ans: The kinetic energy of a gas inside of an enclosed space suggests that the gas particles can move anywhere within that space because of their "Random Motion." Due to this, there is an equal chance of an amount of gas being in all areas of the tyre; suggesting that the pressure is equal at all points on the inside wall of the tyre.

c) More air is pumped into the tyre while the temperature is kept constant until there are twice as many molecules as before. Explain why you would expect the pressure to be doubled.
Ans: The temperature is kept constant and more air is pumped into the tyre until there are twice as many molecules as before. All these molecules collide with each other and against the tyre walls, As the number of molecules are increased which means the pressure will be doubled.

6. Describe the following:
a) What happens to the motion of the molecules of a gas when it cools down?
Ans: If a gas is cooled down, its molecules lose heat; they lose energy and slow down. They move closer to other gas molecules. If we keep cooling down the gas, its particles will eventually stop moving about so fast and form a liquid. This is called condensation.

b) What happens to the motion of a liquid when it cools down?
Ans: If a liquid is cooled down, its molecules lose heat; they lose energy and slow down. They move closer to other liquid molecules. If we keep cooling down the liquid, the molecules in a liquid stop moving about and settle into a stable arrangement, forming a solid. This is called freezing.

Gases and Kinetic theory
7. The pressure on 9 cm³ of oxygen gas is doubled at a fixed temperature. What will its volume become?
Ans: For Solution of Numericals Click Here

8. A container holds 30 m³ of air at a pressure of 150000 Pa. If the volume changed to 10 m³ by decreasing load on the piston. What will the pressure of the gas become? Assume that its temperature remains constant.
Ans: For Solution of Numericals Click Here

9. Air at atmospheric pressure of 760 mm of Hg is trapped inside a container available with a moveable piston. When the piston is pulled out slowly so that the volume is increased from 100 dm³ to 150 dm³, the temperature remaining constant. What will be the pressure of the air becomes?
Ans: For Solution of Numericals Click Here