Enthalpy of vaporization
= Enthalpy of vaporization
{title2=$\Delta H_{\rm vap}$}
The molar <enthalpy> difference between <vapor> and <liquid> at specified conditions, evaluated on coexistence when it is a <latent heat>. Treating it as constant and treating the <vapor> as ideal gives $\ln(P_2/P_1)=(\Delta H_{\rm vap}/R)(1/T_1-1/T_2)$.