
Tiglath M. answered 05/02/16
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UC Berkeley Grad for Chemistry, Organic Chemistry and Biology Tutoring
To find the equilibrium constant you first need to calculate the change in free energy. G is a measure of a system's free energy. The change in free energy is related to delta H and delta S by the following formula
delta G = delta H - T*delta S
Then you can find the equilibrium constant using the following formula.
delta G = -RTln(K) where R, the universal gas constant is 8.314 J/K.mol
As you can see from the above formula the equilibrium constant is related to free energy. The reason is that the equilibrium point occurs where the system has the lowest available free energy. There are three cases that you should know.
Case 1: delta G = 0, K = 1 The system is at equilibrium
Case 2: delta G > 0, K < 1 The equilibrium is closer to the reactants
Case 3: detla G <0, K > 1 The equilibrium is closer to the products
You should notice that this thermodynamic point of view gives the same definition as when just looking at a system from an equilibrium point of view.