Question

Consider the following reaction: 2NO(g)+O2(g)→2NO2(g) Estimate ΔG∘ for this reaction at each of the following temperatures and predict whether or not the reaction will be spontaneous. (Assume that ΔH∘ and ΔS∘ do not change too much within the give temperature range.)

a. 298 K

b. 721 K

c. 853 K

Answer 1

First you need to determine the delta H and delta S for the reaction.

Use delta H formation and delta S formation for this

delta H0 rxn = delta Hf(products) - deltaH(reactants)

= 2 x 33.2 kJ - (2 x 90.2)

= -114 kJ

delta S0 rxn = delta Sf(products) - deltaS(reactants)

= 2 x 240 J - (2 x 210.7 + 205)

= -146.4 J

delta G = delta H - T delta S

At 298 K

delta G = -114000 J - (298 x -146.4)

delta G = -70.37 kJ

At 721 K

delta G = -114000 J - (721 x -146.4)

delta G = -8.44 kJ

At 853 K

delta G = -114000J - (846 x -146.4)

delta G = 9.85 kJ