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