Final answer:
When heat is removed from a gas, the particles move slower and may undergo a phase change to become a liquid.
Step-by-step explanation:
When heat is removed from a gas, the average kinetic energy of the gas particles decreases. This causes the particles to move slower. As a result, the gas may undergo a phase change and become a liquid if it is cooled enough.
For example, when water vapor is cooled, its particles lose kinetic energy and slow down. Eventually, the water vapor condenses into liquid water.
In summary, when heat is removed from a gas, the particles move slower and may undergo a phase change to become a liquid.