Clausius–Clapeyron Calculator

About this calculator

This calculator applies the Clausius–Clapeyron equation to find a substance's vapor pressure at a new temperature from a known reference point: ln(P2/P1) = −(ΔHvap/R)·(1/T2 − 1/T1), where ΔHvap is the molar enthalpy of vaporization and R is the gas constant. It describes how vapor pressure rises steeply with temperature along a liquid's phase boundary.

Chemistry students and chemical/process engineers use it to estimate boiling points at non-standard pressures (such as altitude adjustments or vacuum distillation), and to interpret vapor-pressure data from a reference table or Antoine-equation source. Enter a known temperature/pressure pair, the enthalpy of vaporization, and the target temperature to get the new vapor pressure.