G=h-ts

[MedPR]

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Why does TBR assume temperature is always positive when considering the favorability of the reaction given the sign of H and S?

For instance, for the forward reaction it says:

"S positive, H negative: Favorable at all temperatures."

However, if T is negative, then you could have something like -200-(50)(-10) = +300 value for G.

Is T always positive because it must be in Kelvins and to have negative Kelvin you would need to have -274 C?

 

[theseeker4]

Why does TBR assume temperature is always positive when considering the favorability of the reaction given the sign of H and S?

For instance, for the forward reaction it says:

"S positive, H negative: Favorable at all temperatures."

However, if T is negative, then you could have something like -200-(50)(-10) = +300 value for G.

Is T always positive because it must be in Kelvins and to have negative Kelvin you would need to have -274 C?

Matter doesn't exist at negative Kelvin, which is why 0K is called absolute zero. You can't go below that. T will always be in Kelvin for this reason, so it will always be positive.

To put it another way, temperature is a measure of the amount of heat, and in an object you can't have a "negative" amount of heat (absolute, not relative) so you can't have a negative temperature on an absolute scale.

 

[ljc]

Matter doesn't exist at negative Kelvin, which is why 0K is called absolute zero. You can't go below that. T will always be in Kelvin for this reason, so it will always be positive.

To put it another way, temperature is a measure of the amount of heat, and in an object you can't have a "negative" amount of heat (absolute, not relative) so you can't have a negative temperature on an absolute scale.

This. There is no such thing as negative kelvin.

Temperature measures how much molecules are moving. At 0 Kelvin, they are not moving at all. There is no way to make them move less, because they already aren't moving! 0 Kelvin is a somewhat arbitrary designation as "the point of least/no movement," so there is no way to pass it and go negative. By definition, 0 is the lowest end of the spectrum possible.

And yes, to answer your question, T must always be in Kelvin, because the units of Entropy are J/K, so if you want the 1/K to cancel (leaving you with J), T must be in units K.

 

[MedPR]

Alright, thanks guys.

I knew that absolute 0 = 0K and that you can't have negative Kelvin (I promise, I knew that). I guess I just got lost in the equation and forgot about that fact.