The effect of temperature on the liquid-vapor surface tension of fluorocarbon and hydrocarbon compounds starting from van der Waals interactions (calculated according to Lifshitz's theory) is studied. The correlation obtained is based on the reversibility of the process of separation of two liquid slabs, creating an intermediate vapor phase. The resulting surface tension can be expressed as a function of two surface potentials having simple dependences on temperature. Reasonable distances of closest approach between the slabs are obtained for all cases, including dispersion contributions between the molecules of water as a special case.