As we know that, ΔH=ΔU+ΔngRT
where, ΔU= change in internal energy Δng= number of moles of gaseous products
- number of moles of gaseous reactants =2−0=2 R= gas constant =2cal
But, ΔU=2.1kcal =2.1×103cal[∵1kcal=103cal] ∴ΔH=(2.1×103)+(2×2×300)=3300cal
Now, ΔG=ΔH−TΔS ⇒ΔG=(3300)−(300×20) ⇒ΔG=−2700cal ∴ΔG=−2.7kcal