Presentation on theme: "What does the word equilibrium mean to you? Warm Up."— Presentation transcript:
What does the word equilibrium mean to you? Warm Up
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? 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?
Vocabulary Reversible Reaction Chemical Equilibrium Equilibrium Position Equilibrium Constant, K eq Le Chateliers Principle (later)
Khans Academy Chapter Introduction to Kinetics/Reaction Rates Chapter Reversible Reactions and Equilibrium
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
Equilibrium Position AB (20%)(80%) A B (20%) Equilibrium does not mean 50:50!
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
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
Solving for K eq Moles of B Moles of D Concentration of B (M)
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 ]
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?
What K eq Tells Us If Keq > 1; More products at equilibrium If Keq < 1; More reactants at equilibrium
Cool Down What is the equilibrium expression for this reaction?