## Question 9.63

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

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

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

Samantha Man 1L
Posts: 63
Joined: Fri Sep 28, 2018 12:22 am

### Question 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) SO2(g). " How do I determine stability based off of Gibbs free energy values?

Nicolette_Canlian_2L
Posts: 77
Joined: Fri Sep 28, 2018 12:25 am
Been upvoted: 1 time

### Re: Question 9.63

I'm having trouble with this one as well. What is the relationship between gibbs free energy and stability? Do we have to consider the other thermodynamic terms as well?

Kate_Santoso_4F
Posts: 72
Joined: Fri Sep 28, 2018 12:29 am

### Re: Question 9.63

You can determine which of the following compounds are stable with respect to decomposition into their elements by analyzing their standard free energies of formation. Compounds with a positive free energy of formation are unstable with respect to the elements. Since PCl5 (g) and SO2 (g) have negative standard free energies of formation, they are thermodynamically stable.