What is vapor pressure?

Vapor pressure is defined as the pressure exerted by a vapor in equilibrium with its liquid or solid form at a given temperature. This concept is crucial in understanding how liquids transition to gases and how this relates to temperature and pressure in various systems.

At a certain temperature, molecules of a liquid gain enough energy to escape into the vapor phase until the rate of evaporation equals the rate of condensation. At this point, the vapor pressure is established, representing the equilibrium between the liquid or solid state and its vapor. The vapor pressure can vary significantly depending on the type of substance and its temperature. For example, volatile substances have higher vapor pressures at lower temperatures compared to less volatile substances.

The other choices do not accurately describe vapor pressure. While the first option discusses gas pressure, it lacks the specific context of equilibrium with a liquid or solid form. The third option refers to atmospheric pressure's effect on the boiling point, which is related but distinct from the definition of vapor pressure. The fourth option incorrectly describes the pressure difference between vapor and solid states, which does not encapsulate the concept of vapor pressure accurately. Understanding vapor pressure is essential for analyzing processes such as distillation, evaporation, and various applications in chemical engineering and process operations.