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2012 topic 7.1

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2012 topic 7.1

  1. 1. IB Chemistry Power Points Topic 7 Equilibriumwww.pedagogics.ca Topic 7.1
  2. 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 products and some chemical reactions are reversible! Equilibrium looks at the extent (of completion) of a reversible chemical reaction.
  3. 3. Equilibrium: the extent of a reaction Equilibrium = no observable changes over time In chemistry we encounter two types of equilibrium systems.Physical/phase equilibrium Chemical equilibriumH2O (l) H2O (g) N2O4 (g) 2NO2 (g)
  4. 4. Equilibrium: the extent of a reaction Equilibrium = no observable changes over time In chemistry we encounter two types of equilibrium systems.Physical/phase equilibriumH2O (l) H2O (g)
  5. 5. Equilibrium: the extent of a reaction Equilibrium = no observable changes over time In chemistry we encounter two types of equilibrium systems.Physical/phase equilibrium Chemical equilibriumH2O (l) H2O (g) N2O4 (g) 2NO2 (g)
  6. 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 constant for example • Colorless N2O4 decomposes to brown NO2 at room temperature. The reaction 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. 7. Key concept 1: at equilibrium, concentrations are constant
  8. 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 reaction 2 NO2(g) N2O4(g). This is the reverse reactionThe double arrow implies the process is reversible. N2O4(g) 2NO2(g)
  9. 9. Key concept 2: at equilibrium, forward rate = reverse rate N2O4(g) 2 NO2(g) 2 NO2(g) N2O4(g) “dynamic” implies that at equilibrium the reaction continues in both directions

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