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Topic: Spontaneous Reactions and energy?  (Read 5186 times)

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AdamC637

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Spontaneous Reactions and energy?
« on: April 26, 2005, 12:16:32 AM »
Does energy change always positive for spontaneous reaction?

I think yes because then (d)entropy = (d)H/T, so if entropy is always positive for spont. rxn, then (d)heat of rxn must also always be positive!

I'm not sure though...
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Offline Borek

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Re:Spontaneous Reactions and energy?
« Reply #1 on: April 26, 2005, 05:19:59 AM »
dG = dH + TdS

is what counts.

Thus even if dH < 0 but TdS is large enough, dG > 0 and the reaction is spontaneous.

dS = dH/T only if dG = 0.
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Demotivator

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Re:Spontaneous Reactions and energy?
« Reply #2 on: April 26, 2005, 11:48:38 AM »
Actually, dG = dH - TdS
it's spontaneous for dG < 0.
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Re:Spontaneous Reactions and energy?
« Reply #3 on: April 26, 2005, 06:31:19 PM »
Quote from: Demotivator on April 26, 2005, 11:48:38 AM
Actually, dG = dH - TdS
it's spontaneous for dG < 0.

Oops :-[
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