Gibbs free energy and work??? Non-pv work?

[GomerPyle]

Hello everyone.

I had a question regarding gibbs free energy (EK 1001 chemistry, questions 411-413).

I don't understand why/how gibbs free energy change of a reaction is the maximum energy that the reaction will release to do NON-PV WORK. What is meant by NON-PV work in a chemical reaction, and what does this have to do with gibbs free energy? I have no idea how to relate these concepts. If anybody could provide an example so I can "picture" these concepts, I would appreciate it.

Also, can somebody help me understand why a negative gibbs free energy requires constant pressure and temperature to indicate a spontaneous reaction????

I just need help "picturing" these types of situations so I can understand it. Experiment examples? I am not a big fan of memorizing these things...I want to understand it.

I appreciate it, thanks.

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[GomerPyle]

Nobody??

 

[LoLCareerGoals]

I think PV work is more about physical changes of the substance, taking those out of the equation allows us to focus on the chemical energetics instead.

As for const temp, it is part of the dG expression. If temp varies in dG versus time, then dG too becomes a function of time. I know it is only an algebraic explanation, but it is a way to keep things from getting too complicated (remove another variable). If dG was allowed to be a function of time AND say reaction had kinetics comparable to time span dG was changing over, keeping track of anything would be a nightmare.
I don't have a comparable explanation for pressure, but I am sure the big picture concept is the same -> remove another variable to isolate effects due to reaction chemistry only.

 

[idontcaureuknow]

Did this for a friend earlier. It's a demonstrative derivation, not exactly practical. But it should provide a mathematical answer.