Presentation on theme: "What does the word equilibrium mean to you?"— Presentation transcript:
1 What does the word equilibrium mean to you? Warm UpWhat does the word equilibrium mean to you?
2 Chapter 18.2 Reversible Reactions and Equilibrium Darren DressenChemistry CPLos Altos High School
3 Key Concepts/TasksWhat 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?
7 Equilibrium is a dynamic process … the reaction does not stop Chemical EquilibriumAt 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 stopsEquilibrium is a dynamic process … the reaction does not stop
8 A B A B Equilibrium Position Equilibrium does not mean 50:50! (20%) (80%)AB(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 reactionKr 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 KeqMoles of BMoles of DConcentration 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 equilibriumConcept 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?