Using the ideas from the temperature dependence of the vapor pressure we can make a new equation that relates the vapor pressure, \(P_1\), at one temperature, \(T_1\), to the vapor pressure, \(P_2\), at another temperature, \(T_2\), we find the following (after some algebra).
\[\ln \left({P_2\over P_1}\right) = {\Delta H_{\rm vap}\over R}\left({1\over T_1} - {1\over T_2}\right)\]
This is the Claussius‐Clapeyron Equation. There are many forms in which you might find this equation, however they are all equivalent.
Note: This also means that if you plot \(\ln(P)\) vs \(1/T\) the graph will be a straight line with a slope equal to \(\Delta H_{\rm vap}/ R \).
Derivation of the Claussius-Clapeyron equation assume that the vapor behaves as an ideal gas such that its molar free energy (chemical potential) is simply given as
\[G = G^{\circ} + RT\ln\left ( {P \over P^{\circ}} \right )\]
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