🌡️ Vapor Pressure Calculator – Clausius-Clapeyron
Use the Clausius-Clapeyron equation to estimate a liquid’s vapor pressure at a new temperature, given one known vapor pressure/temperature pair and its enthalpy of vaporization.
What is the Clausius-Clapeyron equation?
The Clausius-Clapeyron equation describes how a liquid’s vapor pressure changes with temperature, based on how much energy (enthalpy of vaporization) is needed to turn the liquid into a gas.
How this calculator works
The two-point form of the equation used here is:
ln(P2/P1) = −(ΔHvap/R) × (1/T2 − 1/T1)
where P1 and T1 are a known vapor pressure and its absolute temperature, P2 is the vapor pressure at the new absolute temperature T2, ΔHvap is the molar enthalpy of vaporization, and R is the gas constant (8.314 J/(mol·K)). The calculator converts your Celsius inputs to kelvin and your enthalpy from kJ/mol to J/mol automatically, then solves the rearranged equation for P2.
This approach assumes ΔHvap stays roughly constant over the temperature range considered, which is a good approximation over moderate temperature spans but becomes less accurate far from the reference point. This tool is for general chemistry education purposes.