# Clausius-Clapeyron Equation

Written by Jerry Ratzlaff on . Posted in Thermodynamics

Clausius-Clapeyron equation is the vapor pressure of given liquids or solids.  This allows us to estimate the pressure temperature, if the vapor pressure is known at some temperature and if the enthalpy of vaporization is known.

## Clausius-Clapeyron Equation

 $$\large{ In \; \left( \frac {p_2}{p_1} \right) = \frac {\Delta H}{R} \; \left( \frac {1}{T_1} - \frac {1}{T_2} \right) }$$

### Where:

 Units English Metric $$\large{ \Delta H }$$ = enthalpy of vaporization of the liquid $$\large{\frac{Btu}{lbm}}$$ $$\large{\frac{kJ}{kg}}$$ $$\large{ p_1 }$$ = vapor pressure at the temperature $$\large{\frac{lbf}{in^2}}$$ $$\large{\frac{kg}{m-s^2}}$$ $$\large{ p_2 }$$ = vapor pressure at the temperature $$\large{\frac{lbf}{in^2}}$$ $$\large{\frac{kg}{m-s^2}}$$ $$\large{ R }$$ = real gas constant $$\large{\frac{lbf-ft}{lbmol-R}}$$ $$\large{\frac{J}{kmol-K}}$$ $$\large{ T_1 }$$ = temperature at which the vapor pressure is known $$R$$ $$K$$ $$\large{ T_2 }$$ = temperature at which the vapor pressure is to be found $$R$$ $$K$$ 