Question

# Explain the following : (a) The surrounding becomes pleasantly warm when water in a lake starts freezing in cold countries. (b) The heat supplied to a substance during its change of state does not cause any rise in its temperature.

Solution

## The correct option is (a) The molecules of liquids will have more kinetic energy than molecules of solid. Solids particles have less Kinetic energy and vibrate about their mean position. So, when the water which is in the liquid state, freezes ( converting water to ice) then it releases the heat to the surroundings. It is an exothermic process where heat is released to surroundings.  Hence, the surrounding becomes pleasantly warm when water in a lake starts freezing in cold countries. (b) The temperature of any substance remains constant during the change of state because the heat energy supplied is used up in changing the state of matter and also this heat is used for breaking of several bonds or attractive forces. This heat, which does not raise the temperature of the body, is called Latent heat.

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