1. Keq vs. Q
Period 2
Sandra

2. When do you do this?
Keq - Is used to provide information about the mixture of reactants and products at equilibrium.
Q – Is use to determine if a reaction is at equilibrium

3. Definitions
Keq - The ratio depicting the concentrations when chemical equilibrium is reached and express the extent to which equilibrium has favored in either direction.
Q – Determines if the reaction is at equilibrium.

4. Rules/Steps
To determine if a reaction is at equilibrium, you need to calculate the reaction quotient(Q) and compare it to the equilibrium constant.
You use the concentrations that the problem provides.
Set it up just as you would set up a Keq expression. Q=product/reactant
Solve
Look at the answer and determine whether the reaction is at equilibrium.
To determine if the reaction is at equilibrium Keq has to equal Q.

5. Example COCl2 ↔ CO + Cl2 Keq = 170
Concentrations: CO and Cl2 are each 0.15M and COCl2 is 1.1 * .001
Q = [CO] [Cl2] / [COCl2]
Q = (0.15)(0.15) / (1.1 * .001) = 20
Q < Keq thus the reaction is not at equilibrium and proceeds to the right.

6. Example Problem
N2 + 3H2 ↔ 2NH3
NH3 = 0.15M
N2 = M
H2=.10M

7. Answer
Keq = [Nh3]2