Temperature dependence of ΔS°, ΔG° and ΔH°

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etotheipi
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I was taught that standard ΔS°, ΔG° and ΔH° are the corresponding quantities measured under standard conditions which I was told was 0.1M for solutions, 1 bar for gases, but importantly also at 298K.

On many places on the internet, however, I have read that 298K is not actually a standard condition. Instead, we can find values for ΔS°, ΔG° and ΔH° for all temperatures.

This makes sense, since considering the definition of ΔG°, for instance,

ΔG° = ΔH° - TΔS°

it would be silly for ΔG° to be fixed at 298K considering that we can choose T to be whatever we want. I thought it should be read more like "The standard change Gibbs energy at e.g. 500K is ΔH° (at 500K) subtract 500K x ΔS° (at 500K).

A common approximation at my level is that ΔH° and ΔS° don't change with temperature, so when calculating ΔG° we can still use the values of ΔH° and ΔS° for 298K. However, this ΔG° would correspond to the reaction under standard conditions at the specified temperature.

I was wondering if anyone could check if I am understanding this correctly? Thank you :)
 

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  • #2
DrDu
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0.1M for solutions is unusual but may be common in some specialized field.
Even if you take Delta H0 and Delta S0 to be independent of temperature, Delta G0 will be temperature dependent because of the T in -T Delta S0, you are right, here.
 

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