apor pressure is a term used in chemistry to describe the pressure exerted by the vapor phase of a substance in equilibrium with its liquid or solid phase at a given temperature. It is the pressure at which a substance transitions from its liquid or solid state to a gaseous state, or vice versa, in a closed system.

When a liquid or solid is exposed to a closed system, some of its molecules or atoms escape from the surface and enter the vapor phase. These molecules or atoms exert a certain pressure on the walls of the container, known as the vapor pressure. The higher the temperature, the more molecules or atoms have sufficient energy to overcome the intermolecular forces and escape into the vapor phase, resulting in an increased vapor pressure.

Vapor pressure is an important property of substances, as it affects various phenomena such as boiling point, evaporation rate, and condensation. It is often used to determine the volatility and purity of liquids, as well as to understand the behavior of substances in different conditions.

Vapor pressure can be measured experimentally using various techniques, such as the use of manometers or instruments specifically designed for this purpose. The results are typically presented in units of pressure, such as atmospheres (atm), millimeters of mercury (mmHg), or pascals (Pa).