1. Reaction Equilibrium

2. Heterogenous vs. Homogenous Reactions
Homogeneous reaction – all reactants and products are in one phase
All in the gaseous phase, or
All in solution (aqueous)
H2O (g) + CO (g)  H2 (g) + CO2 (g)
Heterogeneous reaction – reactants in two phases
Zn(s) + 2HCl(aq)  H2(g) + ZnCl2(aq)

3. The Equilibrium Condition
Equilibrium – the exact balancing of two processes, one of which is the opposite of the other
Ex: the rate of evaporation = rate of condensation

4. Chemical equilibrium – a dynamic state where the concentrations of all reactants and products remain constant
The forward and reverse reactions of a reversible reaction take place at the same rate

6. The Equilibrium Constant: An Introduction Law of chemical equilibrium
For a reaction of the type:
aA + bB  cC + dD
A, B, C, & D are chemical reactants/products
a, b, c, d are the coefficients in the balanced equation

7. Equilibrium expression:
K is the equilibrium constant (also Ke or Keq)
Is a ratio of product concentrations over reactant concentrations
Each concentration is raised to a power corresponding to its coefficient in the balanced equation!!

8. Example
Write the equilibrium expression for the following reaction:
H2 (g) + F2 (g)  2HF (g)
K =

9. Example
Using the equilibrium expression we wrote in the previous slide if: [H2] = 1.000M [F2] = 2.000M K = [HF] = 3.000M

10. Heterogeneous Equilibria
an equilibrium system where the products and reactants are not all in the same state
When solving for K, do not include the concentrations of solids and liquids
The concentrations of solids and liquids cannot change, so are not included in K
Only include the gases and solutions (aqueous) when solving for K.

11. CaCO3(s) ↔ CaCO(s) + CO2(g) PCl5(s) ↔ PCl3(l) + Cl2(g)
Example
CaCO3(s) ↔ CaCO(s) + CO2(g) PCl5(s) ↔ PCl3(l) + Cl2(g)