The exothermic reaction 2NO2(g) <=> N2O4(g), is spontaneous...

Question

at what temperature?

high or low?

Answer 1

∆G = ∆H - T∆S

If ∆G is negative, the reaction will be spontaneous. So, find a temperature that makes ∆G negative.

Since the rx is exothermic, that tells us that ∆H is negative

Since the reaction goes from 2 mols of gas on the left to 1 mol gas on the right, that tells us that ∆S is negative

So, a low temperature would make the term -T∆S a lower value and since it is a negative term this would tend to make ∆G negative.

So, when both ∆H and ∆S are negative, the reaction is spontaneous at LOW temperatures.