Question

Predict under what temperatures (all temperatures, low temperatures, or high temperatures), if any, the reactions will be spontaneous or nonspontaneous.

Part A) N2(g)+O2(g)→2NO(g) ΔH∘rxn=+182.6kJ

Part B) 2N2(g)+O2(g)→2N2O(g) ΔH∘rxn=+163.2kJ

Part C) 4NH3(g)+5O2(g)→4NO(g)+6H2O(g) ΔH∘rxn=−906kJ

Answer 1

We can predict whether a reaction is spontaneous or not by the sign of delta G

delta G = delta H - T delta S

Thus temperature, signs of delta H and delta S determine the spontaneity of reactio.

Delta S in turn depends n the number of moles of gaseous products and reactants.

A) The reaction is

N2(g) +O2(g) ----> 2NO(g)

here there s no change in number of moles of gases, thus delta S =0

but delta H is positive. Thus the reaction is non-spontaneous at all temperatures.

B) 2N2 (g) + O2(g) --> 2N2O(g) delta h is +ve and delta S also positive as number of moles of gased decresed.(2-3)

Hence the reaction as delta G positive at all temperatures and non-spontaneous at all temperatures.

C) In this reaction number of gaseous moles of producs (10) is more than reactants (9). thus delta S is positive.

and delta H is negative. Thus for this reation , delta G is negative at all temperatures and hence spontaneous at all temperatures.