1. Equilibrium
Ms. Hoang ACP Chemistry

2. Concept of Equilibrium
As a system approaches equilibrium, both the forward and reverse reactions are occurring.
At equilibrium, the forward and reverse reactions are proceeding at the same rate.

3. System at Equilibrium
Once Equilibrium is achieved, the amount of each reactant and product remains constant
Think of a seesaw

4. Equilibrium Constant
Ratio between concentration of products and concentration of reactants.
aA+bB ↔cC+dD
K= C c D d A a B b

5. Equilibrium Constant
Example: Calculate the value of the equilibrium constant, K , for the system shown, if moles of CO2, moles of H2, moles of CO, and moles of H2O vapor were present in a 2.00 L reaction vessel were present at equilibrium.
C O 2 g + H 2 g ↔C O g + H 2 O g

6. Equilibrium Constant CO2 0.1908 moles H2 0.0908 moles CO 0.0092 moles
H2O moles
C O 2 =
H 2 =
CO =
H 2 O =
C O 2 g + H 2 g ↔C O g + H 2 O g

7. Equilibrium Constant
K= CO H 2 O C O 2 H 2 = (0.0046)(0.0046) (0.0954)(0.0454) =
If K>1 reaction favors the products
If K<1 reaction favors the reactants

8. What Does the Value of K Mean?
If K >> 1, the reaction is product-favored; product predominates at equilibrium.

9. What Does the Value of K Mean?
If K << 1, the reaction is reactant-favored; reactant predominates at equilibrium

10. Equilibrium Constant Equilibrium is temperature dependent
At the same temperature, the system always comes to an equilibrium position such that K is constant regardless of the amounts of the reactants that are mixed together initially

11. Heterogeneous Equilibria
CaC O 3 s ↔CaO s +C O 2 (g)
Pure solids and liquids (except H2O) are not included in calculations of K

12. Energy and Equilibrium
Which one has higher energy?

13. Energy and Equilibrium
Energy of NO2 at 298K is 51.30kJ/mol
Energy of N2O4 at 298K is 97.82kJ/mol
N2O4
NO2