The free energy, which has a symbol of ΔG° at standard conditions has the formula:
ΔG° = n(ΔH° - TΔS°)
For NaBr:
ΔG° = (1 mol)[(-1 kJ/mol)(1000 J/1 kJ) - (298 K)(57 J/mol·K)]
ΔG° = -17,986 J
For NaI:
ΔG° = (1 mol)[(-7 kJ/mol)(1000 J/1 kJ) - (298 K)(74 J/mol·K)]
ΔG° = -29,052 J