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 (-5[1])at the triple point of water. Mayer’s relation equates this (10[1])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[3])temperature, and the natural log of (10[1])the (10[1])equilibrium (-5[1])constant (10[2])gives the (10[2]-5[2])change in (10[1])Gibbs free (10[1]-5[2])energy (10[1])at standard (10[4]-5[1])conditions. (10[1])This quantity equals the (0[1])product of (10[2])Boltzmann’s (10[1]-5[2])constant (-5[1])and Avogadro’s (10[2]-5[1])number. For (10[3])10 (10[2])points, name this constant (10[1])equal to (10[3])8.314 (10[2]-5[2])joules per mole (10[6])kelvin, symbolized (10[2])R. (10[6])■END■