What is required for vapor to transition to a liquid state?

The transition of vapor to a liquid state, known as condensation, requires the removal of heat. When a vapor cools down, the kinetic energy of the vapor molecules decreases, allowing them to come closer together and form intermolecular bonds. This process releases energy in the form of heat.

In many refrigeration and air conditioning systems, this principle is utilized. For example, in a refrigeration cycle, vapor refrigerant is compressed, which raises its pressure and temperature. The vapor then passes through the condenser where heat is extracted from it. As the vapor loses heat, it condenses into a liquid at a relatively constant pressure.

High pressure, low temperature, and increased volume may influence the condensation process or the physical state of a refrigerant, but heat removal is the fundamental requirement for the vapor to condense into a liquid.