Exercise 5 : Question 7 (72)

Answer the following:

a. What is meant by latent heat? How will the state of matter transform, if latent heat is given off?
→ The heat absorbed or given out by a substance during its transition from one state to another is known as latent heat. If the latent heat is given off, the substance will change from gaseous to liquid or from liquid to solid state. 2 Marks
b. Which principle is used to measure the specific heat capacity of a substance?
→ ‘The Principle of Heat Exchange’ is used to measure the specific heat capacity of a substance. The principle can be stated as follows: If a system of two (or more) objects is kept isolated from the environment such that no heat can enter of exit the system, then, Heat lost by hot body = Heat gained by cold body. 2 Marks
c. Explain the role of latent heat in the change of state of a substance?
→ When a solid body is heated, initially its temperature increases. The heat absorbed by the body is used in increasing the kinetic energy of the particles of the body, as well as for doing work against the forces of attraction between them. As the heating is continued, at a certain temperature (melting point), solid starts getting converted into liquid. While this conversion is taking place, the temperature remains constant and the heat given is used for weakening the bonds between the atoms and molecules. This is called the latent heat of fusion. The same reasoning holds good when a substance goes from a liquid state to a gaseous state. 2 Marks
d. On what basis and how will you determine whether air is saturated with vapour or not?
→ The extent of water vapour present in the air determines whether the air is saturated with water vapour or not. If the relative humidity of air is 100%, it is saturated with water vapour. In such a case, we can see the formation of water droplets on cold bodies such as leaves of plants/grass, glass window panes etc. 2 Marks