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Topic: Thermodynamics  (Read 388 times)

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Offline lonehavoc

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Thermodynamics
« on: April 14, 2021, 05:57:12 PM »
Hello all, I have a question about spontaneous and nonspontaneous reactions. I came across the idea that (at any temperature) as long as Enthalpy change is negative and Entropy change is positive the reaction will "always be spontaneous." I know that if Gibbs free energy is negative then the reaction is considered spontaneous, so what if the temperature is negative, wouldn't that make the statement false?

Offline Corribus

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Re: Thermodynamics
« Reply #1 on: April 14, 2021, 06:17:54 PM »
Temperature is in Kelvin so by definition can't be negative.
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Offline sjb

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Re: Thermodynamics
« Reply #2 on: April 15, 2021, 01:55:40 AM »
Temperature is in Kelvin so by definition can't be negative.

For the purposes of this, this is probably acceptable but negative absolute temperatures are possible in theory.

Offline Meter

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Re: Thermodynamics
« Reply #3 on: April 15, 2021, 04:09:42 AM »
Temperature is in Kelvin so by definition can't be negative.

For the purposes of this, this is probably acceptable but negative absolute temperatures are possible in theory.
I'd like to hear more about this. It was my impression that T < 0 K implied negative entropy?

Offline Borek

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Re: Thermodynamics
« Reply #4 on: April 15, 2021, 04:25:51 AM »
I'd like to hear more about this. It was my impression that T < 0 K implied negative entropy?

https://en.wikipedia.org/wiki/Negative_temperature

The way I see it is that the problem stems from the way temperature is defined. We often define physical properties/quantities using terms we are accustomed to (that is: we observe at more or less STP). These definitions sometimes fail at extremes and produce nonsensical numbers. It typically means we should reconsider our understanding of the phenomena and refine the definition.

@lonehavoc - none of that applies to your question, for your needs Corribus' comment is spot on.
« Last Edit: April 15, 2021, 06:28:50 AM by Borek »
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Offline Corribus

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Re: Thermodynamics
« Reply #5 on: April 15, 2021, 08:39:57 AM »
Temperature is in Kelvin so by definition can't be negative.

For the purposes of this, this is probably acceptable but negative absolute temperatures are possible in theory.

Clearly outside thie scope of the question. You have to have an awareness of what level a student is at.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

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