Clausius-Clapeyron equation

Definition

The Clausius-Clapeyron equation describes the relationship between the vapor pressure and temperature of a substance. It is used to characterize phase transitions, such as from liquid to gas.

5 Must Know Facts For Your Next Test

1. The Clausius-Clapeyron equation can be expressed as $\frac{dP}{dT} = \frac{L}{T(V_{g} - V_{l})}$, where $L$ is the latent heat of transition, $T$ is temperature, and $V_{g}$ and $V_{l}$ are the molar volumes of gas and liquid phases.
2. A simplified form for phase change from liquid to vapor is $\ln P = -\frac{\Delta H_{vap}}{R} \left( \frac{1}{T} \right) + C$, where $\Delta H_{vap}$ is the enthalpy of vaporization and $R$ is the universal gas constant.
3. The equation assumes that the volume of the liquid phase is negligible compared to the volume of the gas phase.
4. It applies primarily to first-order phase transitions, where there is a discontinuous change in entropy and volume.
5. Helps in predicting boiling points at different pressures and understanding how pressure affects phase changes.

Review Questions

• What does the Clausius-Clapeyron equation describe?
• How can you express the Clausius-Clapeyron equation for a liquid-to-vapor transition?
• Why does the Clausius-Clapeyron equation assume that liquid phase volume is negligible?

Related terms

Latent Heat: The amount of heat required to change a substance's phase without changing its temperature.

Vapor Pressure: The pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature in a closed system.

Enthalpy of Vaporization ($\Delta H_{vap}$): The energy required to convert one mole of a liquid into vapor without a temperature change.