Here's why:

* Heat causes a substance to transition from a liquid to a gas. This is called evaporation or boiling. The added heat energy provides the molecules with enough kinetic energy to break free from the liquid's surface and become a gas.

* Cooling causes a gas to condense into a liquid. This is the reverse process of evaporation. As the gas loses energy, the molecules slow down and come closer together, eventually forming liquid bonds.

In summary:

* Heat: Liquid → Gas

* Cooling: Gas → Liquid