Chapter 16, Problem 16.87SP

Sulfur dioxide in the effluent gases from coal-burning electric power plants is one of the principal causes of acid rain. One method for reducing SO₂ emissions involves partial conversion of SO₂ to H₂S, followed by catalytic conversion of the H₂S and the remaining SO₂ to elemental sulfur:

$2{\text{H}}_{\text{2}}\text{S}\left(g\right)+{\text{SO}}_2\left(g\right)\to 3\text{S}\left(s\right)+2{\text{H}}_{\text{2}}\text{O}\left(g\right)$

Using the data in Appendix B, calculate AG° and show that this reaction is spontaneous at 25 °C. Why does this reaction become nonspontaneous at high temperatures? Estimate the temperature at which the reaction becomes nonspontaneous.