When a substance changes state, such as from solid to liquid or liquid to gas, what happens to its energy?

• A. The energy of the substance remains unchanged during a phase change.
• B. Energy is always lost by the substance during any phase change.
• C. Energy is only gained when a substance changes from liquid to solid.
• D. The substance absorbs or releases energy, depending on the direction of the phase change.

Answer: (D)

Verified step by step guidance

1. Understand that during a phase change, the temperature of a substance remains constant while it absorbs or releases energy.
2. Recognize that energy involved in phase changes is called latent heat, which is the energy required to change the phase without changing temperature.
3. Know that when a substance changes from solid to liquid or liquid to gas, it absorbs energy (endothermic process).
4. Know that when a substance changes from gas to liquid or liquid to solid, it releases energy (exothermic process).
5. Conclude that the energy of the substance changes during a phase change by either absorbing or releasing energy, depending on the direction of the change.