1. EQUILIBRIUM

2. EQUILIBRIUM Equilibrium occurs when, in a reaction
reactants form products
AND
products reform reactants
at the same rate
Equilibrium is symbolized by using a double-headed arrow in the chemical equation. ⇄

3. EQUILIBRIUM CO(g) + H2O(g) ⇄ CO2(g) + H2(g) [CO] or [H2O]
Time
Concentration

4. EQUILIBRIUM The blue graph shows the reactants being used up.
[CO] or [H2O]
Equilibrium
[CO2] or [H2]
Time
Concentration
The blue graph shows the reactants being used up.
The red graph shows the products being produced.
At the dotted line, equilibrium is achieved.
At equilibrium, the reaction “stops”.
The forward and reverse reactions are occurring at the same rate.

5. xREACTANTS ⇄ yPRODUCTS
EQUILIBRIUM
Details about the amount of substances can be calculated using the EQUILIBRIUM CONSTANT:
For the reaction:
xREACTANTS ⇄ yPRODUCTS
[ ] mean “concentration (in molarity) of” whatever is inside them
If there is more than one reactant, the concentration of each reactant is taken to its own exponent, then all are multiplied.
If there is more than one product, the concentration of each product is taken to its own exponent, then all are multiplied.

6. EQUILIBRIUM
If you have more than one reactant or product, their concentrations are multiplied in the equilibrium constant:
2A + 3B ⇄ C
Construct the equilibrium constant expression for the above reaction at equilibrium.
Remember, coefficients in the balanced equation become exponents in the equilibrium constant.
[C]
Keq =
[A]2
[B]3

7. EQUILIBRIUM
Solids and liquids do not appear in the equilibrium constant expression. Only gases and dissolved substances appear in the expression.
2A(s) + 3B(g) ⇄ C(g)
Construct the equilibrium constant expression for the above reaction at equilibrium.
[C]
Keq =
[B]3

8. EQUILIBRIUM Interpreting Keq:
If Keq > 1, then the reaction favors more product formation.
If Keq < 1, then the reaction favors more reactant formation.

9. EQUILIBRIUM Relationship to Acids/Bases:
Weak acids/bases have a Keq value that can be calculated.
Strong acids/bases have a Keq that is infinitely large. They dissociate completely leaving no reactant in solution.