1. Free Energy and the
Equilibrium Constant K (Pt 8)
By Shawn P. Shields, Ph.D.
This work is licensed by Shawn P. Shields-Maxwell under a Creative Commons
Attribution-NonCommercial-ShareAlike 4.0 International License.

2. G and the Equilibrium Constant K
Without derivation, the
relationship between the Gibbs
free energy and the equilibrium
constant K is
∆G°
= −RT lnK

3. G and the Equilibrium Constant K
We can obtain the value of the
equilibrium constant K using G
K = 𝑒−
∆G°
RT

4. G and the Equilibrium Constant K
∆G° = −RT lnK
When G < 0, the value for K > 1
(products are favored)
When G > 0, the value for K < 1
(reactants are favored)
When G = 0, the value for K = 1 and
the reaction is at equilibrium.

5. G and the Equilibrium Constant K
∆G° = −RT lnK
Recall that G means the reaction is
under standard conditions.
(1 atm pressure for gases and 1 M
concentration for solutions)

6. G and the Equilibrium Constant K
∆G° = −RT lnK
There is only one value for G for a
given reaction, and the reaction must
have gone to completion.
What if there is a mixture of
reactants and products (i.e., the
reaction didn’t go to completion)?

7. The Difference Between G and G
G always has the same value for a
particular reaction and is calculated
using tabulated data.
G is the actual free energy of the
reaction at a given composition.
What does this mean?

8. The Difference Between G and G
G has a
different
value for each
composition.
G is
minimized at
equilibrium.
“dGdGo" from
http://www.chem1.com/acad/webtext/the
rmeq/TE4.html

9. The Difference Between G and G
Since G is the actual free energy of
the reaction at a given composition, it
changes over the course of the
reaction.
G can be calculated for non-standard
conditions at any point in the reaction.

10. Free Energy for Non-Standard
Conditions (G)
Recall: ∆G°
= −RT lnK
For non-standard conditions, the free
energy change is
∆G = ∆G° + RT ln Q
Where Q is the reaction quotient.

11. IMPORTANT! G versus G
G is for std conditions and always
has the same value for a particular
reaction.
G is the actual free energy of the
reaction at a given composition and
changes over the course of the
reaction (non-standard conditions).

12. Example Problems will be
posted separately 