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### Calculating G if H and S are gven

Posted: Sun Feb 17, 2019 1:09 pm
Can someone please explain why we assume $\Delta$G is 0 when H and S are given?

### Re: Calculating G if H and S are gven

Posted: Sun Feb 17, 2019 1:17 pm
We aren't assuming that the Gibbs Free Energy is equal to 0, rather we are putting in 0 for its value to see when $T\Delta S$ and $\Delta H$ are equal to one another in order to determine at what temperatures the Gibbs Free Energy would be negative (spontaneous reaction) or positive (non spontaneous reaction).

### Re: Calculating G if H and S are gven

Posted: Sun Feb 17, 2019 2:51 pm
If we have the value when the system is in equilibrium and delta G =0, then we can find the behavior (in terms of spontaneity) for any temperatures above or below that value.

### Re: Calculating G if H and S are gven

Posted: Sun Feb 17, 2019 8:19 pm
Why can we use the same deltaH and deltaS to calculate deltaG at any temperature? (like in this problem: 9.53 Calculate the change in molar Gibbs free energy for the process NH3(l) --> NH3 (g) at 1atm and (a) 15.0 C; (b) 45. C (see Tables 8.3 and 9.1 for standard enthalpy and entropy of vaporization))

I thought that deltaH and deltaS would be different for different temperatures? Are the changes in enthalpy and entropy for a phase change the same at any temperature?