Favorable Reactions

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Leia_Acosta_1D
Posts: 9
Joined: Wed Nov 18, 2015 3:00 am

Favorable Reactions

Postby Leia_Acosta_1D » Sun Jan 29, 2017 7:44 pm

On page 39 of the course reader, it says

delta S + favors forward processes
delta H+ endothermic does not favor forward process

Can someone please explain why this is the case?

Ranica Hortelano 2D
Posts: 9
Joined: Wed Nov 18, 2015 3:00 am

Re: Favorable Reactions

Postby Ranica Hortelano 2D » Sun Jan 29, 2017 8:16 pm

In order for delta G to be negative (which entails that the reaction is spontaneous) you want delta S to be positive. If delta S is negative, the whole equation, delta H minus T times delta S, would be positive; delta G would be positive, thus the reaction would be non spontaneous.
For delta S, if you have a reaction that has more molecules/moles of product than reactants, then you have an increase in entropy.
When you have a forward process for delta H you are creating more product (formation of bonds) and so there is a release of energy; delta H is negative because energy is released and we want delta H to be positive if we want a spontaneous reaction.
As long as your -T times delta S term is a large negative number and delta H is positive, your delta G will be negative, hence spontaneous.


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