What is vapor pressure in relation to its liquid or solid phase?

Vapor pressure is defined as the pressure exerted by the vapor of a substance in equilibrium with its liquid or solid phase at a specified temperature. This means that in a closed system, when a liquid or solid is present, some molecules will escape into the gaseous phase, increasing the pressure of the vapor until a balance is reached. At this point, the rate of molecules escaping from the liquid or solid equals the rate of molecules returning to it, resulting in a stable vapor pressure.

Understanding this concept is crucial in various applications such as distillation, evaporation, and understanding phase changes. For example, as temperature increases, vapor pressure also typically increases because more molecules have enough energy to break free from the liquid or solid phase. This dynamic equilibrium is essential for predicting the behavior of substances under changing temperatures and pressures.