Question

What happens to ΔG° (becomes more negative or more positive) for the following chemical reactions when the partial pressure of oxygen is increased?

a) Becomes more negative
b) Becomes more positive
c) No change in ΔG°
d) Depends on the reaction conditions

Answer 1

The change in ΔG° when the partial pressure of oxygen is increased depends on the reaction. For the formation of SO2 from sulfur and oxygen, ΔG° becomes more negative. For the decomposition of HgO, ΔG° becomes more positive.

Step-by-step explanation:

When the partial pressure of oxygen is increased in a chemical reaction, the change in the standard free energy change, ΔG°, depends on the direction in which the reaction shifts to re-establish equilibrium. For the reaction S(s) + O2(g) → SO2(g), an increase in the partial pressure of oxygen will shift the equilibrium toward the products according to Le Châtelier's principle.

This results in an increased equilibrium constant, K, which causes ΔG° to become more negative, indicating the reaction is more spontaneous under those conditions. Conversely, in the decomposition of HgO(s) → Hg(l) + O2(g), increasing the partial pressure of oxygen shifts the equilibrium toward the reactants, leading to a more positive ΔG°, thus the reaction becomes less spontaneous.