We are given the reaction:
NH3(s) → NH3(l)
NH3(s):ΔHf= –46.11 kJ; ΔSf=192.45 J/K
NH3(l):ΔHf= –80.29 kJ; ΔSf=111.3 J/K
The formula of the Gibbs' Free Energy ΔG is
ΔG = ΔHf - TΔS
Assume T = 25 degrees C
For NH3(s):
ΔG = –46.11 kJ * 1000 - (192.45 J/K*298K)
ΔG = - 103.460 kJ
For NH3 (l)
ΔG = –80.29 kJ * 1000 - (111.3 J/K*298K)
ΔG = - 113.457 kJ
Therefore the ΔG under standard temperature for the reaction is the difference between the products - reactants. Solve for this.
