1. What does the word equilibrium mean to you?
Warm Up
What does the word equilibrium mean to you?

2. Chapter 18.2 Reversible Reactions and Equilibrium
Darren Dressen
Chemistry CP
Los Altos High School

3. Key Concepts/Tasks
What does chemical equilibrium really mean and how does an equilibrium change with time?
Be capable of writing an equilibrium expression by just looking at a reaction.
What does the value of Keq indicate about the equilibrium position of a reaction?

4. Vocabulary Reversible Reaction Chemical Equilibrium
Equilibrium Position
Equilibrium Constant, Keq
Le Chatelier’s Principle (later)

5. Khan’s Academy Chapter 18.2 - Reversible Reactions and Equilibrium
Chapter Introduction to Kinetics/Reaction Rates
Chapter Reversible Reactions and Equilibrium

6. Reversible Reaction

7. Equilibrium is a dynamic process … the reaction does not stop
Chemical Equilibrium
At chemical equilibrium, no net change occurs in the actual amounts of the components (reactants and products) of the system (chemical reaction).
A common misconception: Once a reaction is at equilibrium everything stops
Equilibrium is a dynamic process … the reaction does not stop

8. A B A B Equilibrium Position Equilibrium does not mean 50:50! (20%)
(80%) A B
(80%)
(20%)
Equilibrium does not mean 50:50!

9. Equilibrium Position: Kf and Kr rate constants
(20%)
(80%)
Kf is the rate constant for the forward reaction
Kr is the rate constant for the reverse reaction

10. Equilibrium Constant, Keq
The equilibrium constant (Keq) is the ratio of product concentrations to reactant concentrations at equilibrium.
Keq is derived from Kf and Kr …..
Keq = Kf/Kr

11. Solving for Keq
Moles of B
Moles of D
Concentration of B (M)

12. Exception Keq = [AgCl]2 [CuCl2]
If a molecule in the reaction is a pure solid or pure liquid, then it is removed from the equilibrium expression.
2Ag(s) + CuCl2(aq) Cu(s) + 2AgCl(aq)
Keq = [AgCl]2
[CuCl2]

13. Why don’t solids and liquids count?
Since concentrations of pure liquids and solids remain constant, these substances can be ignored in equilibrium constant expression.
Known as a heterogeneous equilibrium
Concept question??? What is the difference between a homogeneous and heterogeneous equilibrium?

14. What Keq Tells Us If Keq > 1; More products at equilibrium
If Keq < 1; More reactants at equilibrium

15. Cool Down What is the equilibrium expression for this reaction?