Asked by Robert

Explain why each of the following is incorrect:

(a) Entropy increases in all spontaneous reactions.

Wouldn't (a) be actually correct? Because when there's a spontaneous reaction, you have less stable molecules and more disorder. It will be lower in some reactions than in others, but doesn't it always increase when a reaction favors spontaneity?

Answers

Answered by Robert
So when there's a spontaneous reaction, deltaS is > 0 , I confused that with increase. I still don't see how it's incorrect
Answered by Robert
(b) deltaG < 0 , are product-favored and occur with rapid transformation of reactants to products.

HOw is this incorrect? deltaG < 0 is product-favored and is rxn forward.

Thank you
Answered by DrBob222
For dS, it depends upon what dS you are talking about. dS is positive(increases) for all spontaneous reactions IF you are talking about total dS; i.e.,
dSsurrounds + dSsystem = positive.

For dG, the first part is correct about < 0; the last part makes it incorrect. dG says nothing about how fast a reaction will occur.
Answered by Robert
Thanks Bob! As for deltaS, it just says Entropy increases in all spontaneous reactions, there's nothing more specified, so I assumed that it was deltaS and not deltaSuniverse
Answered by DrBob222
Regarding dS for the system, there are some reactions that occur spontaneously in which dS decreases. Since
dG = dH - TdS, the delta H part may override the TdS part just as in endothermic reactions the TdS part can overcome the dH part.
Answered by Robert
I get it now, thanks again Bob

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