This quantity appears in the denominator of the critical temperature but [emphasize] not the critical pressure in the van der Waals definition. Trouton’s rule approximates the entropy of vaporization of many liquids as approximately 10.5 times this (10[4])quantity. This (10[1])quantity was formerly obtained from measuring the speed of sound in argon at the triple point of water. Mayer’s relation equates this quantity with the difference in two types of molar heat (-5[1])capacities. The (10[1])negative (10[1])product of this (-5[1])quantity, (10[2])temperature, and the natural log of (10[1])the (10[1])equilibrium (-5[1])constant (10[1])gives the (10[2]-5[1])change in (10[1])Gibbs free (10[1]-5[2])energy at standard (10[4]-5[1])conditions. This quantity equals the product of (10[1])Boltzmann’s (10[1]-5[1])constant (-5[1])and Avogadro’s (10[2]-5[1])number. For (10[3])10 (10[1])points, name this constant (10[1])equal to (10[3])8.314 (10[2]-5[2])joules per mole (10[5])kelvin, symbolized (10[2])R. (10[6])■END■