Question

What do we mean by a dynamic equilibrium? Describe how the development of a vapor pressure above a liquid represents such an equilibrium.

Short answer

Dynamic equilibrium is a state where opposing processes occur at equal rates, resulting in no net change in the system, though it is constantly active on a microscopic level. The development of vapor pressure above a liquid represents such an equilibrium, as evaporation and condensation occur simultaneously at equal rates. This constant activity establishes a constant vapor pressure, known as the equilibrium vapor pressure.

Step-by-step solution

Define equilibrium

Equilibrium is a state where opposing forces or reactions occur at the same rate, resulting in no net change in the system. In the context of chemical reactions, this means that the rates of the forward and reverse reactions are equal, and the concentration of the reactants and products remain constant.

Define dynamic equilibrium

Dynamic equilibrium is a specific type of equilibrium in which the opposing processes are continuously occurring, even though there is no overall change in the system. In other words, although it appears that the system is in a stable state, it is constantly active on a microscopic level with processes happening at equal rates.

Vapor pressure and dynamic equilibrium

The development of vapor pressure above a liquid is an example of dynamic equilibrium. When a liquid is placed in a closed container, molecules at the surface of the liquid can gain enough energy to escape from the liquid phase and enter the gas phase, a process called evaporation. At the same time, gas-phase molecules can collide with the surface of the liquid and lose energy, which allows them to rejoin the liquid phase, a process called condensation.

Equilibrium vapor pressure

As the number of gas-phase molecules increases, the likelihood of condensation also increases. Eventually, the rates of evaporation and condensation will become equal, establishing a dynamic equilibrium. At this point, the vapor pressure remains constant and is referred to as the equilibrium vapor pressure. In conclusion, dynamic equilibrium is a state in which opposing processes occur at equal rates, creating an overall appearance of stability even though the system is constantly active. The development of vapor pressure above a liquid is an example of dynamic equilibrium, with evaporation and condensation occurring simultaneously at equal rates, producing a constant vapor pressure.