## 9.65 6th edition writing chemical equations

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

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

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

Helen Zhao 1F
Posts: 31
Joined: Fri Sep 28, 2018 12:20 am

### 9.65 6th edition writing chemical equations

For question 9.65 from the 6th edition, how do you know if the compound is decomposing for forming. For example, how do you know its P + 5/2Cl2 -> PCL5 instead of PCl5 -> P + 5/2Cl2?

Andrea Zheng 1H
Posts: 61
Joined: Fri Sep 28, 2018 12:26 am

### Re: 9.65 6th edition writing chemical equations

You can use either the equation for decomposition or composition, as it will yield the same answer.

As an example, part (a):
If you used the equation of composition, P + 5/2Cl2 -> PCl5, you would find that the entropy of the reaction was negative. This means that at higher temperatures, the reverse reaction is favored. This means that P and Cl2 would be favored, showing that at higher temperatures, the compound is less stable.

If you used the equation of decomposition, PCl5 -> P + 5/2Cl2 , you would find that the entropy of the reaction was positive. This means that at higher temperatures, the forward reaction is favored. This means that P and Cl2 would be favored, showing that at higher temperatures, the compound is less stable.

Hope this helps!