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We are providing you with the best chemistry notes written by Sir Umair Khan. This is the first chapter of Class 10 Chemistry, the book States of Matter and Phase Changes.

All quick checks (Class 10 Chemistry chapter 14)

14.1 Quick Check

1. What is translational motion?
Translational motion is the motion in which particles move from one place to another in straight paths, but may be in random directions.

2. Is the average kinetic energy possessed by the particles of a gas and a liquid the same at the same temperature?
Yes, the average kinetic energy of particles of a gas and a liquid is the same at the same temperature. Kinetic energy is proportional to the absolute temperature (K.E ∝ T), not to the physical state. 

14.2 Quick Check

1. Why does water vapour at 100°C cause more severe burns as compared to liquid water at the same temperature?
Water vapours at 100°C contain extra latent heat of vaporization. When they condense on the skin, they release this heat, causing more severe burns.

2. Why do we feel comfortable wearing cotton clothes in summer?
Cotton clothes absorb sweat and allow it to evaporate easily. Evaporation produces a cooling effect, making us feel comfortable.

14.3 Quick Check

1. Does the change in temperature occur during the process of evaporation?
Yes, a cooling effect is produced during evaporation. During this process, the high kinetic energy particles escape from the surface of the liquid, leaving behind particles with lower kinetic energy. As a result, the average kinetic energy decreases and the liquid becomes cool. Heat is then absorbed from the surroundings.  

2. Does ice sublime?
Yes, ice can sublime slowly under suitable conditions by changing directly from solid into vapour.

3. Give one example each for sublimation and deposition other than those mentioned in the textbook.

• Sublimation: Ammonium chloride changes directly from solid to vapour on heating. 
• Deposition: Formation of snow from water vapour in clouds (vapour directly changes into solid ice crystals). 

14.4 Quick Check

(i) How does a gas exert pressure?

According to kinetic particle theory, gas particles move randomly in all directions. When these particles collide with the walls of the container, they exert force on them, producing pressure.

(ii) How does the volume of a gas change when its temperature is decreased? (Pressure and mass constant)

When the temperature decreases, the kinetic energy of gas particles decreases. The particles move more slowly and come closer together, so the volume of the gas decreases.

14.5 Quick Check

1. Which gas among the following will diffuse at the fastest speed, and which will diffuse at the slowest speed under similar conditions of temperature and pressure?
Gases given: NO₂, SO₂, H₂S

• Fastest diffusion: H₂S
• Slowest diffusion: SO₂

This is because lighter gases diffuse faster than heavier gases.

2. Explain with the help of the kinetic particle theory why ammonia gas diffuses faster than hydrogen chloride gas?
According to kinetic particle theory, lighter gas particles move faster at the same temperature. Ammonia (NH₃) has a lower molecular mass (17g/mol) than hydrogen chloride (HCl), which is 36.5g/mol, so ammonia diffuses faster.

EXERCISE Class 10 Chemistry Chapter 14

A. Multiple Choice Questions

Choose and tick the correct answer from the given choices.

1. According to kinetic theory, the basic difference between solid, liquid, and

gas, is due to:

(a) The difference in the movements of the particles. 

(b) the chemical properties of the particles.

(c) the size of the particles.

(d) the shape of the particles.

2. Upon heating, the rate of evaporation:

(a) decreases

(b) increases

(c) remains the same

(d) initially decreases and then increases upon further heating

3. The inter-particle attractions are the strongest in:

(a) Solids 

(b) Liquids

 (c) Plasma

 (d) Gas

4. Cooling the vapours of some gases change them directly into solid state.

This phenomenon is called:

(a) evaporation  

(b) condensation

(c) sublimation

(d) deposition

5. Physical state in which the particles possess the maximum energy:

(a) Solid 

(b) Liquid

(c) Gaseous 

(d) Vapour

6. How does the process of evaporation depend on the force of attraction

present among the molecules of a liquid?

(a) It decreases with the increasing strength of attraction.

(b) It increases with the increasing strength of attraction.

(c) It is independent of the strength of the force of attraction.

(d) It first increases and then decreases with the increasing strength of the force of attraction.

7. Which gas will diffuse at the fastest rate?

(a) HCl  

(b) SO₂

(c) H₂S

(d) CO₂

8. The phase changes A and B in 

gas→A→ liquid→B→ solid are:

(a) Melting, evaporating 

(b) Condensation, melting

(c) Condensation, freezing 

(d) Boiling, freezing

9. A student noticed frost falling on the ground at 6.30 am and disappearing

by 8.30 am. Which phase change was responsible for changing the frost into water vapour?

(a) Melting  

(b) Evaporation

(c) Sublimation 

(d) Deposition

B. Short Answer Questions

14.1 From where does the energy come when a liquid evaporates?
The energy required for evaporation comes from the inner high kinetic energy molecules and their surroundings. The liquid particles absorb heat energy and escape into the air as vapours.

14.2 Is condensation an endothermic process?
No, condensation is an exothermic process. During condensation, gas particles lose heat energy and change into liquid.

14.3 Why do naphthalene balls (used to repel insects) disappear after some time?
Naphthalene balls disappear because they undergo sublimation. They directly change from solid state into gas without becoming liquid.

14.4 Why does the temperature remain constant during a phase change?
During a phase change, the heat energy is used to change the state of matter instead of increasing temperature. Therefore, the temperature remains constant until the change is complete.

14.5 Is it possible to compress a liquid like a gas?
No, liquids cannot be compressed easily like gases because the particles in liquids are already closely packed together.

14.6 Can you change the temperature at which water boils in an experiment in your lab?
Yes, the boiling point of water can be changed by changing pressure. Lower pressure decreases the boiling point, while higher pressure increases it.

14.7 In which season do wet clothes get dry after a relatively longer time?
Wet clothes dry more slowly in the winter or rainy season because the temperature is lower and the air contains more moisture.

14.8 When a solid is heated, what happens to its particles which are vibrating?
When a solid is heated, its particles gain kinetic energy and vibrate more rapidly about their fixed positions.

14.9 Do solids and liquids also diffuse just like gases?
Yes, solids and liquids also diffuse, but much more slowly than gases because their particles move less freely.

14.10 Why is dew formed in the early hours of the morning?
Dew is formed because water vapours in the air cool down and condense into tiny water droplets on cool surfaces during early morning.

C. Constructed Response Questions

14.1 Differentiate between evaporation and boiling.

14.2 Describe how boiling is related to the external pressure?

Boiling occurs when the vapour pressure of a liquid becomes equal to the external pressure. If the external pressure decreases, the liquid boils at a lower temperature. If the external pressure increases, the boiling point increases.

14.3 Why does the process of evaporation not need the input of energy?

Evaporation does not need external heating because liquid particles absorb energy from the surroundings. The high-energy particles escape from the surface into the air.

14.4 Why do the heating and cooling curves for phase changes adopt the same path?

The heating and cooling curves follow the same path because the amount of heat absorbed during melting is equal to the heat released during freezing. Similarly, the heat absorbed during boiling is equal to the heat released during condensation.

14.5 Why does ice melt when pressure is exerted on it?

When pressure is applied on ice, its melting point decreases. As a result, some ice melts into water even at temperatures near 0°C.

14.6 Why do phase changes occur?

Phase changes occur because matter gains or loses heat energy. This changes the motion(K.E) and arrangement of molecules, causing matter to change from one state to another.

D. Descriptive Questions

14.1 Explain the difference in the rates of diffusion of two gases based on kinetic theory.

14.2 How does the process of sublimation helpful in printing and in the usage of air freshener? 

14.3 Draw heating curve for the physical changes water undergoes with change in temperature.