The temperature of a substance does not change during a phase change. It comes as a surprise to many students that the melting point of ice and the freezing point of water are the same. This Powerpoint presentation explains why there is no temperature change as heat is added or removed during a phase change. The presentation illustrates this graphically using a heating curve, and explains how to interpret a heating curve.
Free worksheets for this topic are available on my website at http://evanschemistrycorner.com