Solve for \Delta G at 1000K: NH_{4}Cl Reaction

[Swerting]

Homework Statement

The reaction is NH_{4}Cl(s)\rightarrow NH_{3}(g)+HCl(g)
\Delta H^{o}=+176 kJ and \Delta G^{o}=+91.2 kJ at 298 K
What is the value of \Delta G at 1000 K?

Homework Equations

\Delta G=\Delta H-T\Delta S
The same applies if all 'deltas' are standard

The Attempt at a Solution

Well, I solved for standard change of entropy (\Delta S^{o}) and came up with .284 kJ/K, which is the same when using a table of standard entropies. My problem is, I'm not sure where to go from this to find \Delta G, or even a way to link standard values to normal values for these. I tried plugging in the values for standard delta H and delta S with 1000K to find delta G, but something tells me that this is incorrect. Any help would be greatly appreciated!

-Swerting

 

[Mapes]

Why do you think your first approach is incorrect?

 

[Swerting]

I believe that my first approach is incorrect since standard values are at 298.15K, and this is asking for delta G at 1000K, implying that delta H and delta S have changed as well.

 

[Mapes]

Do you know how to calculate changes in \Delta H and \Delta S with temperature? (Hint: it involves the heat capacity.) Alternatively, you could look up these values at 1000 K.

 

[Swerting]

I can calculate \Delta H from changes in temperature, but unfortuneately, not \Delta S, nor could I find a table of entropies at 1000K.

 

[Swerting]

Alright, well, in the depths of the internet I finally found the answer explained, and apparently my using standard delta H and S were correct. The answers from the company that make the questions say that delta S doesn't change (thought says nothing about delta H) and so I just plug in the values and solve for delta G. Ah well, who would've guessed that values so dependent on temperature don't really change over an actual temperature change. :P
Thank you very much for your help!

-Swerting