Use this reaction for this question:

4NH3 (g) + 2O2 (g) 4NO (g) + 6H2 (g); H = -905 J.

Which statement is true about the reaction above?

A. G is negative at all temperatures.
B. S is negative and G is positive.
C. S is negative and G is negative.
D. G is positive at all temperatures.
E. S is positive and G is positive.

1 answer

dG = dH - TdS.
You know dH is -
You know dS is + (because there are 6 mols gas on the left and 10 on the right; an increase in mols of gas is an increase in S.)
From the above equation if dH is - and dS is +, the term -TdS will be - no matter what T is used so dG will be - at all T.