What is the relationship between thermal energy and the phase of a substance?

The relationship between thermal energy and the phase of a substance is closely connected to the energy required for phase changes and the temperature changes that occur during those transitions. As a substance transitions from one phase to another—such as from solid to liquid (melting) or liquid to gas (evaporation)—thermal energy must be added or removed.

During a phase change, thermal energy is absorbed or released by the substance, but the temperature may remain constant throughout the process until the change is complete. For example, when ice melts to become water, it absorbs thermal energy but does not increase in temperature until all the ice has melted.

Thus, thermal energy does not remain constant during phase changes; rather, it changes depending on the phase and temperature of the substance. This is why the correct answer emphasizes the link between thermal energy and both phase and temperature alterations. Understanding this concept is crucial for grasping principles related to heat transfer, temperature, and the behavior of matter in different states.