Problem 20 - Chemistry An Atoms First Approach

Question

Describe what is meant by a dynamic equilibrium in terms of the vapor pressure of a liquid.

Step-by-Step Solution

Answer

A dynamic equilibrium in terms of the vapor pressure of a liquid occurs when the rates of evaporation and condensation become equal, resulting in a constant vapor pressure for a given temperature in a closed system. This state of balance maintains constant concentrations of liquid and vapor phases, as the number of molecules escaping from the liquid phase into the vapor phase is equal to the number of molecules returning from the vapor phase to the liquid phase.

Step 1: Understanding Dynamic Equilibrium

Dynamic equilibrium occurs when the rate of change in one direction is equal to the rate of change in the opposite direction. It is a state of balance in a reaction where the forward and reverse reactions occur at the same rate, and the concentration of the reactants and the products remain constant over time.

Step 2: Defining Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature in a closed system. In other words, it is the pressure at which the gaseous phase of a substance is in equilibrium with its liquid or solid phase.

Step 3: Connecting Vapor Pressure and Dynamic Equilibrium

A dynamic equilibrium exists between a liquid and its vapor when the rate of evaporation is equal to the rate of condensation. At this point, the vapor pressure remains constant as the number of molecules escaping from the liquid phase into the vapor phase is equal to the number of molecules returning from the vapor phase to the liquid phase. When a liquid is placed in a closed container, some of its molecules will escape and become vapor. As the concentration of vapor molecules above the liquid increases, the chances of these vapor molecules colliding with the liquid surface and returning to the liquid phase also increase. Over time, the rate of evaporation and the rate of condensation will become equal, and the system will reach a state of dynamic equilibrium. In conclusion, a dynamic equilibrium occurs in terms of the vapor pressure of a liquid when the rates of evaporation and condensation become equal, resulting in a stable and constant vapor pressure for a given temperature in a closed system.