When a substance undergoes a phase change from a solid to a liquid the substance can absorb heat energy without undergoing a temperature change. But I also read that when a substance melts, the atoms absorb energy and thereby vibrate faster, overcoming the intermolecular forces. Temperature is defined as the average KE of random translational motion of atoms/molecules of a substance. So if molecules vibrate faster in overcoming intermolecular forces, wouldn't the temperature go up? This contradicts the fact that temperature does not go up during a phase change. Can someone shed some light on this? I'm thinking there is a lot more to phase change on a molecular level. Thanks!