Practice: Vapor pressure measurements at various temperature values are given below. Determine the molar heat of vaporization for cyclohexane.

The **Clausius-Clapeyron Equation** establishes a quantitative relationship between **vapor pressure** and **temperature**.

Concept #1: Understanding the Clasius-Clapeyron Equation

Vapor Pressure looks at the equilibrium established between vaporization and condensation. By using the Clasius-Clapeyron equation, the enthalpy of vaporization can be determined.

Concept #2: Linear Form of Clausius-Clapeyron Equation

Linear Form of Clausius-Clapeyron Equation used when given a plot of lnP vs inverse of Temperature.

Example #1: The vapor pressure of a substance is measured over a range of temperatures. A plot of the natural log of the vapor pressure vs the inverse of the temperatures (in Kelvin) produces a straight line with a slope of -2.79 x 10^{3} K.

Find the enthalpy of vaporization of the substance.

Practice: Vapor pressure measurements at various temperature values are given below. Determine the molar heat of vaporization for cyclohexane.

Concept #3: Two-Point Form of Clausius-Clapeyron Equation

Two-Point Form of Clausius-Clapeyron Equation used when 2 Temperatures and 2 Pressures are involved.

Example #2: The enthalpy of vaporization of water is 40.3 kJ/mol at its normal boiling point at 100ºC. What is the vapor pressure (mmHg) of water at 60ºC?

Practice: Benzene has a heat of vaporization of 30.72 kJ/mol and a normal boiling point of 80.1°C. At what temperature does benzene boil when the external pressure is 405 torr?