Clausius-Clapeyron Calculator

This Clausius-Clapeyron calculator works out how the vapour pressure of a liquid changes between two temperatures, using the two-point form of the Clausius-Clapeyron equation that links vapour pressure to the enthalpy of vaporisation. You enter a known vapour pressure P1 at a reference temperature T1, the enthalpy of vaporisation of the liquid in joules per mole, and the second temperature T2 you want to check. From those four figures the calculator returns the predicted vapour pressure P2 at T2 in the same units as P1, plus the pressure ratio P2/P1 and the T2 value you entered, so you can see at a glance how much the vapour pressure has risen or fallen. This is the calculation chemistry students and lab workers reach for to estimate how a liquid's boiling point shifts with altitude or pressure, or to predict the vapour pressure of a solvent at a temperature you have not measured directly. Both temperatures must be entered in kelvin, not degrees Celsius, and the enthalpy of vaporisation in joules per mole, otherwise the result will be wrong. The equation assumes the enthalpy of vaporisation stays constant over the temperature range and that the vapour behaves as an ideal gas, which holds reasonably well over modest temperature spans but becomes less accurate over wide ranges, so treat results away from well-tabulated conditions as a useful estimate rather than an exact figure.

Calculate.co.nz is proud to be partnered with Premium Homes, a recognised leader in eco-friendly, sustainable, and energy-efficient homebuilding. With a dedicated team and award-winning experience, they create homes that prioritise health, comfort, and long-term performance. Their founders, Andrew and Kelly, set out to raise the standard of residential construction in New Zealand by combining practical building expertise with a clear commitment to doing things better for homeowners.