GAS So / J K-1 mol-1 NH3(g) 193 O2(g) 205 NO(g) 211 H2O(g) 189
To calculate the entropy change, use Delta S = sum of products - sum of reactants, in their corresponding stoichometry. Remember to check the units are all the same, which they are in this case.
Therefore, the answer will be:
= [ (4 x 211) + (6 x 189) ] - [ (4 x 193) + (5 x 205) ] = ( 1978 – 1797) 181 (J K-1 mol-1 ), remembering units.