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

In summary: Why do you think your first approach is incorrect?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.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.I can calculate \Delta H from changes in temperature, but unfortuneately, not \Delta S, nor could I find a table of entropies at 1000K.Alright, well, in the depths of the internet I finally found the answer explained
  • #1
Swerting
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Homework Statement


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


Homework Equations


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


The Attempt at a Solution


Well, I solved for standard change of entropy ([tex]\Delta S^{o}[/tex]) 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 [tex]\Delta G[/tex], 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
 
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  • #2
Why do you think your first approach is incorrect?
 
  • #3
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.
 
  • #4
Do you know how to calculate changes in [itex]\Delta H[/itex] and [itex]\Delta S[/itex] with temperature? (Hint: it involves the heat capacity.) Alternatively, you could look up these values at 1000 K.
 
  • #5
I can calculate [tex]\Delta H[/tex] from changes in temperature, but unfortuneately, not [tex]\Delta S[/tex], nor could I find a table of entropies at 1000K.
 
  • #6
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 dependant on temperature don't really change over an actual temperature change. :P
Thank you very much for your help!

-Swerting
 

1. What is the formula for calculating \Delta G at 1000K for the NH_{4}Cl reaction?

The formula for calculating \Delta G at 1000K for the NH_{4}Cl reaction is: \Delta G_{1000K} = \Delta H_{1000K} - T\Delta S_{1000K}, where \Delta H_{1000K} is the change in enthalpy, T is the temperature in Kelvin, and \Delta S_{1000K} is the change in entropy.

2. What are the values needed to calculate \Delta G at 1000K for the NH_{4}Cl reaction?

The values needed to calculate \Delta G at 1000K for the NH_{4}Cl reaction are the change in enthalpy (\Delta H_{1000K}) and the change in entropy (\Delta S_{1000K}). These values can be obtained from experimental data or calculated using thermodynamic equations.

3. How do temperature changes affect the value of \Delta G for the NH_{4}Cl reaction?

The value of \Delta G for the NH_{4}Cl reaction is directly affected by temperature changes. As the temperature increases, \Delta G decreases, and as the temperature decreases, \Delta G increases. This is because the \Delta S term in the formula becomes more significant at higher temperatures.

4. What does a positive or negative value of \Delta G at 1000K indicate for the NH_{4}Cl reaction?

A positive value of \Delta G at 1000K indicates that the reaction is not spontaneous at that temperature and would require an input of energy to occur. A negative value of \Delta G at 1000K indicates that the reaction is spontaneous at that temperature and would release energy.

5. How can the value of \Delta G at 1000K be used to predict the spontaneity of the NH_{4}Cl reaction?

If the value of \Delta G at 1000K is negative, it indicates that the reaction is spontaneous and will occur without an input of energy. If the value of \Delta G at 1000K is positive, it indicates that the reaction is non-spontaneous and will only occur with an input of energy. Therefore, the value of \Delta G at 1000K can be used to predict the spontaneity of the NH_{4}Cl reaction at that temperature.

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