Question

When water at $0^{\circ }$C freezes to form ice at the same temperature of $0^{\circ }$C, then it :

(a) absorbs some heat (b) releases some heat

(c) neither absorbs nor releases heat (d) absorbs exactly 3.34$\times {10}^5$ J/Kg of heat

Answer 1

option b is the correct answer.

Interestingly, if you add heat (say, by putting the mixture in a warmer environment), the melting ice will absorb the added heat, keeping the mixture at 0C. If you remove heat (by putting the mixture in a colder environment), the freezing water will release heat, keeping the temperature of the mixture constant. As long as there's both water and ice mixed together, the temperature doesn't change.