Answer:
The standard free energy change is -502.86 KJ
Step-by-step explanation:
ΔG° = H° -TΔS°
where;
ΔG° is the standard free energy
H° is the standard enthalpy change = -631 kJ
ΔS° is the standard change in entropy = -430 J/K 
T is the temperature of the system = 25⁰C = 298 K
Applying the formula above;
ΔG° = -631 kJ - ( -0.43J/K × 298K)
 = -631 kJ + 128.14 KJ
 = -502.86 KJ
Therefore, the standard free energy change is -502.86 KJ