College Chemistry : Gibb's Free Energy
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Example Questions
Example Question #3 : Thermodynamics And Kinetics
How do we know if a reaction is spontaneous?
The first law of thermodynamics
The value of 
The second law of thermodynamics
The sign of
The sign of
The sign of
A reaction is spontaneous if and only if 
Example Question #1 : Gibb's Free Energy
What is the standard change in free energy for a reaction run at 
In this question, we're told of a reaction that is run at a given temperature and with a certain equilibrium constant. We're asked to evaluate the standard change in free energy for this reaction.
First, right off the bat, we can see that the equilibrium constant for the reaction is greater than one. As a result, we know that under standard conditions, equilibrium of this reaction will favor products. Hence, we know right away that 
To actually calculate the value of 
If we plug in the values that we know, we can solve for the correct answer.
Example Question #1 : Thermodynamics
Calculate the change in free energy, in kilojoules, of the reaction at 
Recall how to find the change in free energy for a reaction from using free energies of formation:
Where 
Plug in the given values to find the change in free energy for the reaction.
Example Question #2 : College Chemistry
Suppose that a given chemical reaction has an enthalpy change of 
For this question, we're asked to determine the temperature needed for a reaction to be in a state of equilibrium. We are also provided with the entropy and enthalpy changes for this reaction.
Remember that for a reaction to be in a state of equilibrium, the value for its change in free energy must be equal to zero. Furthermore, we can state the relationship between the change in free energy with the change in entropy, the change in enthalpy, and the temperature as follows.
Because the 
Now that we have this expression, we just need to plug in the two values given to us in the question stem. Remember to make the units match though!
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