1.IB Chemistry Power Points Topic 7Equilibriumwww.pedagogics.caTopic 7.1

2. Equilibrium: the extent of a reaction Recall: for a chemical reaction actual yield < theoretical yield Why? Because Reactants are not pure Not all product is recovered Other competing reactions use up reactant to form alternate productsand some chemical reactions are reversible! Equilibrium looks at the extent (of completion) of a reversible chemical reaction. 3. Equilibrium: the extent of a reactionEquilibrium = no observable changes over timeIn chemistry we encounter two types of equilibriumsystems.Physical/phase equilibriumChemical equilibriumH2O (l)H2O (g) N2O4 (g) 2NO2 (g) 4. Equilibrium: the extent of a reactionEquilibrium = no observable changes over timeIn chemistry we encounter two types of equilibriumsystems.Physical/phase equilibriumH2O (l)H2O (g) 5. Equilibrium: the extent of a reactionEquilibrium = no observable changes over timeIn chemistry we encounter two types of equilibriumsystems.Physical/phase equilibriumChemical equilibriumH2O (l)H2O (g) N2O4 (g) 2NO2 (g) 6. Equilibrium: the extent of a reactionA chemical equilibrium is achieved when: the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constantfor example Colorless N2O4 decomposes to brown NO2 at room temperature. Thereaction is reversible.N2O4(g) 2NO2(g). At equilibrium, there is a mixture of N2O4 and NO2. The reaction does not stop. The color remains constant 7. Key concept 1: at equilibrium, concentrations are constant 8. Constant concentrations imply that the forwardreaction must be proceeding at the same rate as thereverse reaction.N2O4(g) 2 NO2(g)This is the forward reaction2 NO2(g)N2O4(g). This is the reverse reactionThe double arrow implies the process is reversible.N2O4(g)2NO2(g) 9. Key concept 2: at equilibrium, forward rate = reverse rate N2O4(g) 2 NO2(g) 2 NO2(g)N2O4(g)dynamic implies that at equilibriumthe reaction continues in both directions