The process of gas transforming into a liquid can be either exothermic or endothermic, depending on the specific circumstances and substances involved. Let's consider two scenarios:
Condensation: When a gas undergoes condensation and transforms into a liquid, this process is typically exothermic. Heat energy is released as the gas particles lose energy and transition into a more ordered and lower-energy liquid state. This release of heat causes the surroundings to warm up. An example of this is when water vapor condenses to form liquid water, such as the formation of dew on a cool surface.
Evaporation and Vaporization: On the other hand, the reverse process, where a liquid transforms into a gas, is typically endothermic. Energy is required to break the intermolecular forces holding the liquid together, allowing the molecules to overcome these forces and transition into a higher-energy gaseous state. This energy is often drawn from the surroundings, resulting in cooling. For instance, when liquid water evaporates or boils to become water vapor, it absorbs heat from the surroundings, leading to a cooling effect.
In summary, the process of gas to liquid (condensation) is generally exothermic, while the process of liquid to gas (evaporation or vaporization) is typically endothermic.