### Equations of delta G

Posted:

**Thu Feb 21, 2019 12:43 am**How do we distinguish when to use delta G = delta H - delta S temperature and delta G = Delta G (product) - Delta G (reaction)?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=135&t=42537

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Posted: **Thu Feb 21, 2019 12:43 am**

How do we distinguish when to use delta G = delta H - delta S temperature and delta G = Delta G (product) - Delta G (reaction)?

Posted: **Thu Feb 21, 2019 2:20 am**

Both can give you the same thing, you just need to look at what you're given and determine which formula has it ex. if you're given delta H, T, and delta S, then you'll want to use delta G = delta H - T delta S

Posted: **Fri Feb 22, 2019 1:00 am**

It is also important to note that you might get slightly different answers when using the two different methods due to rounding differences since you are using a table of information for one and information given in the problem for the other.

Posted: **Fri Feb 22, 2019 9:30 am**

It is usually based on your givens and if you have enthalpy then most likely the first one will be used. It helps to check off what you have and see what you can plug in.

Posted: **Fri Feb 22, 2019 9:39 am**

Don’t forget that there is also this equation: ∆G = ∆G° + RTlnQ A lot of homework questions about Gibbs free energy can only be answered with this. It’s generally used when given a temperature value, a K value, and concentations/partial pressures of reactants and products to calculate Q.