1. Equilibrium -Keq

2. Equilibrium Constants: Keq
Chemists generally express the position of equilibrium in terms of numerical values, not just percent
These values relate to the amounts (Molarity) of reactants and products at equilibrium
This is called the equilibrium constant, and abbreviated Keq

3. Equilibrium Constants
consider this reaction (the capital letters are the chemical, and the lower case letters are the balancing coefficient):
aA + bB  cC + dD
The equilibrium constant (Keq) is the ratio of product concentration to the reactant concentration at equilibrium, with each concentration raised to a power (which is the balancing coefficient).

4. Equilibrium Constants
consider this reaction:
aA + bB  cC + dD
Thus, the “equilibrium constant expression” has this general form:
[C]c x [D]d
[A]a x [B]b
(brackets: [ ] = molarity concentration)
Note that Keq has no units on the answer; it is only a number because it is a ratio
Keq =

5. Equilibrium Constants
When Keq > 1: more product than reactants at equilibrium
When Keq < 1: more reactant than products at equilibrium
In determining Keq, you only look at the concentrations of gases or aqueous solutions. NOT pure solids or liquids.

6. Equilibrium Constants
Keq only changes value at different temperature. NOT when concentrations are changed. When concentrations are changed, the value of the reactants and products may initially change, but you must use the concentration value at equilibtium to calculate Keq.