Clausius-Clapeyron Vapor Pressure – AP Chemistry

Learning Objectives

Determine Vapor Pressure ($P_{vap}$) dynamically as a function of Temperature ($T$).

Observe Enthalpy of Vaporization ($\Delta H_{vap}$) impact.

Extract linearity from the $\ln(P)$ vs $1/T$ plot.

Connect boiling point to atmospheric pressure.

Key Equations

$ \ln \left( \frac{P_2}{P_1} \right) = \frac{-\Delta H_{vap}}{R} \left( \frac{1}{T_2} - \frac{1}{T_1} \right) $

$ \ln(P) = \frac{-\Delta H_{vap}}{RT} + C $

Why It Matters

Vapor pressure represents the equilibrium between liquid and gas states. The Clausius-Clapeyron equation allows chemists to linearize exponential evaporation data, making it easy to determine the intermolecular force strength ($\Delta H_{vap}$) from the plot's slope.