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# increasing temperature of exothermic reactions Watch

1. It says in my book: 'generally you will find that most exothermic reactions are spontaneous, even if entropy decreases (the system becomes more ordered), because enthalpy contributes more to ΔG than does entropy. the exceptions are reactions occurring at high temperatures in which entropy decreases'. I'm mainly confused with the bold part, Are they trying to say exothermic reactions aren't feasible at high temperatures? If so how comes?
2. (Original post by tammie123)
It says in my book: 'generally you will find that most exothermic reactions are spontaneous, even if entropy decreases (the system becomes more ordered), because enthalpy contributes more to ΔG than does entropy. the exceptions are reactions occurring at high temperatures in which entropy decreases'. I'm mainly confused with the bold part, Are they trying to say exothermic reactions aren't feasible at high temperatures? If so how comes?
Look up the equation that relates G to H and S. S becomes more important at high T.
3. (Original post by JMaydom)
Look up the equation that relates G to H and S. S becomes more important at high T.
Is entropy high because more bonds are being made at higher temperatures? I don't understand why this is not feasible
4. (Original post by tammie123)
Is entropy high because more bonds are being made at higher temperatures? I don't understand why this is not feasible
Entropy is a function of both number of particles and the available energy that can be distributed over the particles.

More energy (higher temperature) = more entropy ...
5. (Original post by charco)
Entropy is a function of both number of particles and the available energy that can be distributed over the particles.

More energy (higher temperature) = more entropy ...
Sorry I meant, is entropy low because there are more bonds being made at higher temperatures? I just realized I wrote it wrong (in the comment you just quoted now) because it says in my book 'the exceptions are reactions occurring at high temperatures' (in OP). Even if high temperatures are used just because the entropy decreases why isn't it spontaneous?

6. (Original post by tammie123)
Sorry I meant, is entropy low because there are more bonds being made at higher temperatures? I just realized I wrote it wrong (in the comment you just quoted now) because it says in my book 'the exceptions are reactions occurring at high temperatures' (in OP). Even if high temperatures are used just because the entropy decreases why isn't it spontaneous?

All reactions that proceed whatever the temperature are spontaneous. Non-spontaneous processes cannot occur ...
7. (Original post by charco)
All reactions that proceed whatever the temperature are spontaneous. Non-spontaneous processes cannot occur ...
So could this be what my book is trying to say (in OP): at higher temperatures a lot more bonds are being made and entropy decreases so much that it's not possible for this reaction to occur?
8. (Original post by tammie123)
So could this be what my book is trying to say (in OP): at higher temperatures a lot more bonds are being made and entropy decreases so much that it's not possible for this reaction to occur?
No, I don't think so.

The statement as written doesn't make much sense (or at least, to me)

It seems to be referring to a specific reaction that you have not referenced.
9. (Original post by charco)
No, I don't think so.

The statement as written doesn't make much sense (or at least, to me)

It seems to be referring to a specific reaction that you have not referenced.
I'm referring to the bold bit in this paragraph in my textbook: 'generally you will find that most exothermic reactions are spontaneous, even if entropy decreases (the system becomes more ordered), because enthalpy contributes more to ΔG than does entropy. The exceptions are reactions occurring at high temperatures in which entropy decreases'.

I'm confused about what it could mean, so I was thinking maybe it means that the reason why entropy decreases at high temperatures (leading to the reaction not being feasible) could be because more bonds are made, but it's not possible to make this many bonds. I was just thinking that if there were more bonds being formed then the amount of moles would perhaps decrease leading to a decrease in entropy as more atoms would be clumped together.
10. OK, all they are saying is that Gibbs free energy becomes positive in exothermic reactions when the temperature is high because the term -TΔS becomes greater in magnitude than ΔH.

There have been a lot of posts on this theme lately so I have prepared a couple of things:

Entropy

Gibbs free energy

Check them out ...
11. (Original post by charco)
OK, all they are saying is that Gibbs free energy becomes positive in exothermic reactions when the temperature is high because the term -TΔS becomes greater in magnitude than ΔH.

There have been a lot of posts on this theme lately so I have prepared a couple of things:

Entropy

Gibbs free energy

Check them out ...
Yeah that's what I thought at first but when they said 'entropy decreases' that really confused me. But I'm glad it's finally been cleared up.

Wow! Thanks for the links! They're really useful, this topic is quite hard to grasp but it simplifies it really well

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Updated: April 19, 2013
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