Gibbs Energy of Mixing After mixing, the partial pressures of the gases are pa and pB, where the total pressure is p= pA pB. The total Gibbs energy is then nAHA +RT In pa+nBluB+RT In pal The difference in Gibbs energies, Gr -Gi, is the Gibbs energy of mixing n,rt In +nRT II IX We use mole fractions, replacing ny with Xn IX nRT( In B Since the mole fractions are never greater than 1 the In terms are negative and Ami g<o This allows is to conclude that mixing processes are spontaneous, and gases mix spontaneously in 08 all proportions Molo fraction of A. x