Which of the following best defines vapour pressure in a liquid?

Explanation:

Vapour Pressure:

• Vapour pressure is a fundamental concept in the study of liquids and their phase transitions. It is defined as the pressure exerted by the vapour in equilibrium with its liquid at a given temperature. This means that at a specific temperature, a certain number of liquid molecules will have enough kinetic energy to escape the liquid phase and enter the vapour phase, creating a dynamic equilibrium where the rate of evaporation equals the rate of condensation.
• When a liquid is placed in a closed container, molecules continuously move between the liquid and vapour phases. Initially, the rate of evaporation exceeds the rate of condensation because there are few molecules in the vapour phase. As more molecules enter the vapour phase, the rate of condensation increases. Eventually, a state of equilibrium is reached where the number of molecules evaporating equals the number of molecules condensing. The pressure exerted by the vapour at this equilibrium state is called the vapour pressure.

Factors Affecting Vapour Pressure:

• Temperature: Vapour pressure increases with temperature because higher temperatures provide more energy for molecules to escape the liquid phase.
• Nature of the Liquid: Different liquids have different vapour pressures at the same temperature. For example, volatile liquids like ether have higher vapour pressures compared to less volatile liquids like water.