The Clausius-Clapeyron equation predicts the temperature dependence of vapor pressures of pure liquids or solids:
where P is the vapor pressure, P° is a vapor pressure at a known temperature T°, H is an enthalpy of vaporization if the substance is a liquid or an enthalpy of sublimation if it's a solid, R is the ideal gas law constant , and T is the temperature (in kelvins).