Question

(a) Explain why there is no rise in temperature of a substance when it undergoes a change of state although it is still being heated.
(b) Name one property which is shown by naphthalene and not by sodium chloride.

Answer 1

(a) Once the change in state of a substance starts (solid to liquid or liquid to gas), th etemperature of the substance does not change. Actuallym the heat energy now supplied does not increase the kinetic energy of the constituting particles. It is absorbed either as latent heat of fusion or as latent heat of vaporisation.
(b) Napthalene undergoes sublimation upon standing /heating and directly changes into vapours. Sodium chloride (common salt) does not undergo sublimation. It melts on strong heating.