HEAT – 10th Class – Chemistry

1. Define the term temperature.
A. Temperature can be defined as the ‘degree of hotness or coldness’. It is a measure of thermal equilibrium.

2. How does sweat cools our body during evaporation?
A. When we work our bodies produce heat. As a result the temperature of the skin increases and water in the sweat glands evaporate from the body. This evaporation cools the body and it regulates the body temperature.

3. Define the term heat?
A. Heat is a form of energy that flows from a body at higher temperature to a body at lower temperature.

4. Define the term calorie?
A. The amount of heat required to raise the temperature of 1 gram of water by 1°C is called calorie. (Here in calorie ‘c’ should be in small because it indicates gram calorie. Capital C in calorie indicates food Calorie which is equal to 1000 gram calories) 1 calorie = 4.186 Joules

5. What do you mean by evaporation?
A. The process of escaping of molecules from the surface of a liquid at any temperature is called evaporation.

6. Write about the factors that affect the rate of evaporation?
A. The factors that affect the rate of evaporation are surface area, temperature and amount of water vapour already present in the surrounding air.

7. Define condensation?
A. Condensation can be defined as “The change of phase from gas to liquid”.

8. What is humidity?
A. The amount of water vapour present in air is called humidity.

9. Explain about the formation of dew?
A. During winter nights, the atmospheric temperature falls down. The air near to the surfaces will be saturated with vapour and condensation begins. The water droplets condensed on such surfaces
are known as ‘dew’.

10. Explain the formation of fog?
A. During winter nights, if the temperature falls further, the whole atmosphere in that region contains a large amount of vapour and the water molecules present in vapour condenses on dust particles in air and form small droplets of water. These droplets keep floating in the air and form a thick mist which restricts visibility. This thick mist is called as fog.

11. Distinguish between boiling and boiling point?
A. Boiling: “Boiling is a process in which the bulk of the liquid from liquid phase changes to gaseous phase at a constant temperature and constant pressure”.
Boiling point: The temperature at which the liquid boils is called the boiling point of the liquid.

12. Define the term latent heat of vaporization?
A. Latent heat of vaporization can be defined as the amount of heat energy required to change 1 gram of liquid to gas at constant temperature. Its CGS units: cal/gm and SI units: J/Kg.

13. Distinguish between melting and melting point?
A. Melting: “The process in which solid phase changes to liquid phase at a constant temperature is
called melting”. Melting point: This constant temperature is called melting point.

14. Define the term Latent heat of fusion?
A. Latent heat of fusion can be defined as the amount of heat energy required to convert 1 gram of solid completely into liquid at a constant temperature.

15. Write about freezing?
A. Freezing: “The process in which a substance in liquid phase changes to solid phase by losing some of its energy is called “freezing”.