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Warm Up

Warm Up. What does the word equilibrium mean to you?. Chapter 18.2 Reversible Reactions and Equilibrium. Darren Dressen Chemistry CP Los Altos High School. Key Concepts/Tasks. What does chemical equilibrium really mean and how does an equilibrium change with time?

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Warm Up

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

  2. Chapter 18.2Reversible 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 18.1 - Introduction to Kinetics/Reaction Rates Chapter 18.2 - 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 A B (20%) (80%) A B (80%) (20%) Equilibrium does not mean 50:50!

  9. Equilibrium Position:Kf and Kr rate constants Kf A B kr (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 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? What is the equilibrium expression for this reaction?

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