How this calculator works
Choose a temperature-change calculation for a pure substance, or an ideal-solution calculation at one temperature. Clausius-Clapeyron assumes constant vaporization enthalpy and ideal vapour; it becomes less accurate over wide intervals or near the critical point. Raoult law assumes a nonvolatile solute and an ideal solvent; the pure and solution pressures must refer to the same temperature. Use absolute pressure and consistent reference states.
Formula
ln(P2/P1) = -(Hvap/R)(1/T2 - 1/T1). For an ideal solution with nonvolatile solute, Psolution = xsolvent Ppure.
Worked example
At unchanged temperature, an initial vapour pressure of 10 kPa remains 10 kPa. At one fixed temperature, solvent mole fraction 0.5 and pure vapour pressure 10 kPa give solution pressure 5 kPa.
Advertisement
Frequently asked questions
Can I apply both effects?
First estimate pure-solvent pressure at the new temperature, then apply the solution mole fraction at that temperature.
Does the solution pressure include volatile solute?
No. A volatile solute needs its own partial-pressure contribution.
What if pressures fall when temperature rises?
That is inconsistent with a positive vaporization enthalpy in this pure-substance model.