Calcium Oxide is used to remove pollutant SO2 from smokestack gases. The ΔG° of the overall reaction is - 418.6 kJ. What is PSO2 in equilibrium with air (PO2 = 0.21 atm) and solid CaO?

CaO (s) + SO2 (g) + 1⁄2O2 (g) ⇔CaSO4 (s)

From the change in free energy, we can calculate the equilibrium constant by the equation ΔG°=-RT ln (K) where K is the equilibrium constant.

-418.6x10^2 = - (8.314) (298) ln (K)

K = 2.38x10^73

K is expressed as:

K = 1 / Pso2 (Po2) ^0.5 = 1 / Pso2 (0.21) ^0.5

2.38x10^73 = 1 / Pso2 (0.21) ^0.5

Pso2 = 9.17x10^-74 atm