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) 298K

B) 733K

C) 853K

Answer 1

For this reaction delta H0 and delta S0 are positive as we can know this is endothermic reaction and entropy also increases as more number of gaseous products are formed.

delta G0 = delta H0 - T(delta S0)

so delta G0 becomes negative i.e spontaneous at high T value as Tdelta S0 crosses the value of delta H0

and as delta H0 and delta S0 values remains almost same so at high temperaures Reaction is spontaneous and non-spontaneous at low temperature

So at 298K it must be non-spontaneous where as at 733K and 853K it will be spontaneous.