Presentation on theme: "What does the word equilibrium mean to you?"— Presentation transcript:
1What does the word equilibrium mean to you? Warm UpWhat does the word equilibrium mean to you?
2Chapter 18.2 Reversible Reactions and Equilibrium Darren DressenChemistry CPLos Altos High School
3Key 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?
7Equilibrium 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
8A B A B Equilibrium Position Equilibrium does not mean 50:50! (20%) (80%)AB(80%)(20%)Equilibrium does not mean 50:50!
9Equilibrium 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
10Equilibrium 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
11Solving for KeqMoles of BMoles of DConcentration of B (M)
12Exception 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]
13Why 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?
14What Keq Tells Us If Keq > 1; More products at equilibrium If Keq < 1; More reactants at equilibrium
15Cool Down What is the equilibrium expression for this reaction?