In Section 11.5, we defined the vapor pressure of a liquid in terms of an equilibrium. (b) By using data in Appendix B, give the value of Kp for this reaction at 30 C.

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Identify the chemical reaction for the vaporization of a liquid, which is typically: \( \text{liquid} \rightleftharpoons \text{vapor} \).

Understand that the equilibrium constant \( K_p \) for this reaction is related to the vapor pressure of the liquid at a given temperature.

Use the data in Appendix B to find the vapor pressure of the liquid at 30°C.

Recognize that the vapor pressure of the liquid at equilibrium is equal to the partial pressure of the vapor, which is used to calculate \( K_p \).

Express \( K_p \) as the vapor pressure of the liquid at 30°C, since \( K_p = P_{\text{vapor}} \) for this equilibrium.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature. It reflects the tendency of particles to escape from the liquid phase into the vapor phase. The higher the temperature, the greater the vapor pressure, as more molecules have sufficient energy to overcome intermolecular forces.

Equilibrium Constant (Kp)

The equilibrium constant (Kp) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a gas-phase reaction, with each concentration raised to the power of its stoichiometric coefficient. Kp is temperature-dependent and provides insight into the extent of a reaction; a larger Kp indicates a greater concentration of products at equilibrium.

Temperature Dependence of Kp

The value of Kp varies with temperature due to changes in the kinetic energy of molecules and the equilibrium position of the reaction. For endothermic reactions, Kp increases with temperature, while for exothermic reactions, Kp decreases. Understanding this relationship is crucial for predicting how changes in temperature affect the equilibrium state of a reaction.

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