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

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Presentation on theme: "What does the word equilibrium mean to you? Warm Up."— Presentation transcript:

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

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 K eq indicate about the equilibrium position of a reaction?

4 Vocabulary Reversible Reaction Chemical Equilibrium Equilibrium Position Equilibrium Constant, K eq Le Chateliers Principle (later)

5 Khans Academy Chapter Introduction to Kinetics/Reaction Rates Chapter Reversible Reactions and Equilibrium

6 Reversible Reaction

7 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 Equilibrium Position AB (20%)(80%) A B (20%) Equilibrium does not mean 50:50!

9 Equilibrium Position: K f and K r rate constants AB (20%)(80%) KfKf krkr K f is the rate constant for the forward reaction K r is the rate constant for the reverse reaction

10 Equilibrium Constant, K eq The equilibrium constant (K eq ) is the ratio of product concentrations to reactant concentrations at equilibrium. K eq is derived from K f and K r ….. K eq = K f /K r

11 Solving for K eq Moles of B Moles of D Concentration of B (M)

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

13 Why dont 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 K eq 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?

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