Step 1: Use Gibbs free energy relation for electrochemical cell.
\[
\Delta G^0 = -n F E^0_\text{cell}
\]
where \(n\) = number of electrons transferred, \(F = 96485\, \text{C/mol}\).
Step 2: Identify \(n\).
For P\(^0\)/P\(^{3+}\) and Q\(^{2+}\)/Q, assume overall 2 electrons transferred.
Step 3: Calculate \(\Delta G^0\).
\[
\Delta G^0 = -(2)(96485)(0.2) \approx -38594\, \text{J} \approx 115.8\, \text{kJ}
\]
Step 4: Final conclusion.
\[
\boxed{115.8\, \text{kJ}}
\]