Reactions in the Solid Phase

This section discusses the equilibrium of reactions in the solid phase. The activity of solids which do not form solid solutions equals 1, and the reaction proceeds in the direction of decrease in the Gibbs energy until at least one of the reacting substances disappears from the mixture. The reactants are in equilibrium with the products only if ∆rG• = 0. Solid solutions are processed in the same way as liquids.

Questions

1. Can red and white phosphor be in equilibrium at 298 K and 101.325 kPa if you know that under these conditions the molar Gibbs energies of the pure substances are G•m,1 = −6.804 kJ mol−1 and G•m,2 = 5.2 kJ mol−1?
2. What is the value of ∆rG for the reaction 0 = P(red,s) − P(white,s)?

Answers

1. No, red and white phosphor cannot be in equilibrium at 298 K and 101.325 kPa. The molar Gibbs energy of red phosphor is lower than the molar Gibbs energy of white phosphor, so the reaction will proceed until all white phosphor transforms into red phosphor.
2. The value of ∆rG for the reaction 0 = P(red,s) − P(white,s) is −12.004 kJ mol−1.