Anonymous
Anonymous asked in Science & MathematicsChemistry · 8 years ago

How is Gibbs sandard free energy definied at other temperatures?

I am so confused.I was taught that gibbs standrd free energy (G°) is defined at 298k (25C) and 1 atmosphere.But then I know that delta G° =-RT ln K. So G° changes with temperature? If G° is defined at 25C then it doesnt make sense to say that G° changes with a raise in temp..In one question it asks me to calculate K at 327C given delta H standard and standard entropy.By delta G° = delta H° − T delta S° I see that G° changes with temp but I though G° is always a constant for a given reaction.Please elaborate in simple words as much as possible.Thank you!

Update:

I know what the first responder said but as I said in my text book it says that G° changes with temperature!How is it possile

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  • 8 years ago
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    deltaG° is used for reactions at 25°C and 1 atm pressure.

    deltaG (notice no degree symbol) at any other temperature must be found by using the standard delta H° and Standard deltaS° (meaning 25°C and 1atm pressure).

    Delta G = Delta H° - T(Delta S°)

    depending on what your delta H° and Delta S° are, the temperature can either lower or increase your delta G

    ex.

    If H = - and S = +, then a higher temperature will give you a more negative delta G AT THAT TEMPERATURE, meaning the reaction is spontaneous AT THAT TEMPERATURE.

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