What happens to heat energy when a substance undergoes a phase change?

When a substance undergoes a phase change, heat energy is absorbed or released without causing a change in temperature. This process occurs because the energy is used to break or form intermolecular bonds rather than to increase kinetic energy, which is what raises temperature.

For instance, during melting, heat is absorbed to transition from solid to liquid, and during boiling, heat is absorbed to change from liquid to gas. In both cases, the temperature remains constant as the energy is directed toward facilitating the change in state. This concept is fundamental in thermodynamics and is crucial for understanding how energy transfers between different states of matter.

The other options do not accurately describe the behavior of heat energy during phase changes.