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Calculating G if H and S are gven

Posted: Sun Feb 17, 2019 1:09 pm
by Kimberly 1H
Can someone please explain why we assume 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
by whitney_2C
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 and 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
by 005199302
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
by annabel 2A
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?