Question

Consider the reaction: 2NO(g)+ O 2 (g)→2 NO 2 (g) Estimate Δ G ∘ for this reaction at each temperature and predict whether or not the reaction will be spontaneous. (Assume that Δ H ∘ and Δ S ∘ do not change too much within the given temperature range.)

Part A

298 K

Part B

714 K

Part C

852 K

Answer 1

part A)

ΔHo = Δ Ho products - Δ H ∘ reactants

= (2 x 33.18) - ( 2 x 90.25 + 0)

= --114 kJ / mol

Δ S∘ = Δ S∘ products - Δ S∘ reactants

= 2 x 240.0 - ( 2 x 210.6 + 205 )

= -146.2 J / K

Δ G∘ = ΔHo - T Δ S∘

= -114 - 298 x (-0.1462 )

= -70.4 kJ / mol

Δ G∘  = -70.4 kJ / mol

Δ G∘ value is neagtive so the reaction is spontaneous

part B)

Δ G∘ = ΔHo - T Δ S∘

= -114 - 714 x (-0.1462 )

= -9.61 kJ / mol

Δ G∘  = --9.61 kJ / mol

Δ G∘ value is neagtive so the reaction is spontaneous

part C)

Δ G∘ = ΔHo - T Δ S∘

= -114 - 852 x (-0.1462 )

= 10.6 kJ / mol

Δ G∘  = 10.6 kJ / mol

Δ G∘ value is positive so the reaction is not spontaneous