When a substance transitions from a liquid to a gas, what generally happens to its molecular energy?

When a substance transitions from a liquid to a gas, the process involves an increase in molecular energy. This is primarily because the molecules in the liquid state have less energy compared to when they are in the gaseous state.

In the liquid phase, molecules are close together and have enough energy to move past one another, but they are still held together by intermolecular forces. As the liquid is heated or otherwise provided with energy—usually in the form of heat—the molecules gain kinetic energy. This increased kinetic energy allows them to overcome the attractive forces keeping them in the liquid state.

Once sufficient energy is absorbed, the molecules can break free from the liquid and enter the gas phase, where they move more freely and are spaced further apart. The increased motion and spacing of gas molecules correspond to a higher energy state compared to their liquid counterparts. Thus, the transition from liquid to gas is associated with an increase in molecular energy, making that choice the correct one.