## 9.63

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

CaminaB_1D
Posts: 63
Joined: Fri Sep 28, 2018 12:16 am

### 9.63

9.63 Determine which of the following compounds are stable with respect to decomposition into their elements under standard conditions at 25 C (see Appendix 2A): (a) PCl5(g); (b) HCN(g); (c) NO(g); (d) SO (g).

After calculating the standard free energy of formation of the compounds, why does a positive value mean the compound is unstable with respect to its elements (b and c). Why does a negative value (a and d) mean the compounds are thermodynamically stable if they are spontaneous?

Sarah Kiamanesh 1D
Posts: 30
Joined: Fri Sep 28, 2018 12:22 am

### Re: 9.63

Positive values denote instability because it means that the reverse reaction is spontaneous. the reactants are produced more than the products are.
Negative values denote stability because the forward reaction is stable. the products are spontaneously produced.