The table below shows standard entropies, S⊖S^\ominusS⊖, for three gases.
| Substance | S⊖S^\ominusS⊖ / J mol−1K−1\text{J mol}^{-1}\text{K}^{-1}J mol−1K−1 |
|---|---|
| NH3(g)\text{NH}_3(\text{g})NH3(g) | 192.8 |
| N2(g)\text{N}_2(\text{g})N2(g) | 191.6 |
| H2(g)\text{H}_2(\text{g})H2(g) | 130.7 |
What is the entropy change, ΔS⊖\Delta S^\ominusΔS⊖, in J mol−1K−1\text{J mol}^{-1}\text{K}^{-1}J mol−1K−1, for the catalytic decomposition of ammonia shown below?
2NH3(g)→N2(g)+3H2(g) 2\text{NH}_3(\text{g}) \rightarrow \text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) 2NH3(g)→N2(g)+3H2(g)−198.1-198.1−198.1
+129.5+129.5+129.5
+198.1+198.1+198.1
+390.9+390.9+390.9
