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 18.1 - Introduction to Kinetics/Reaction Rates Chapter 18.2 - 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?