ΔH=ΔU+ΔngRT
=2.1×103+2(2)(300)
=2100+1200
=3300cal
ΔG=ΔH−TΔS
=3300−(300)(20)
=3300−6000
=−2700cals=−2.7kcal
Gibbs free energy can be visualized as the amount of useful energy present in a thermodynamic system that can be utilized to perform some useful work.