Clapeyron Equation

Name:
Clapeyron Equation
Detailed information:
The equation dp/dT = ΔH/TΔV. It states that the rate of change of vapor pressure of a liquid (expressed in ergs per cubic centimeter) with absolute temperature (in Kelvins) equals the heat of vaporization (in ergs per gram) divided by the product of the absolute temperature and the increase in volume (V, in cubic centimeters) when a gram of the liquid changes to vapor. Other consistent units may be used. The approximate Clapeyron equation, dlnp/dT = ΔH/RT², expresses the same relation in a less-exact form because in its derivation, it is assumed that ΔV is equal to the volume of vapor. This assumption (that the volume of liquid is negligibly small) is usually true within a few percent under ordinary conditions of temperature and pressure.