(
课件网) Chapter 15 Chemical Equilibrium Chemical Equilibrium 15 15.1 The Concept of Equilibrium 15.2 The Equilibrium Constant Calculating Equilibrium Constants Magnitude of the Equilibrium Constant 15.3 Equilibrium Expressions Heterogeneous Equilibria Manipulating Equilibrium Expressions Gaseous Equilibria 15.4 Using Equilibrium Expressions to Solve Problems Predicting the Direction of a Reaction Calculating Equilibrium Concentrations 15.5 Factors that Affect Chemical Equilibrium Addition or Removal of a Substance Changes in Volume and Pressure Changes in Temperature Catalysis The Concept of Equilibrium The decomposition of N2O4 is a reversible process, meaning the products of the reaction can react to form reactants. The system is in equilibrium when the rates of the forward reaction and the reverse reaction are the same. rate forward = kf[N2O4] and rate reverse = kr[NO2]2 15.1 N2O4(g) 2NO2(g) The Concept of Equilibrium Starting with N2O4 The Concept of Equilibrium Starting with NO2 The Concept of Equilibrium Some important things to remember about equilibrium are: Equilibrium is a dynamic state—both the forward and reverse reactions continue to occur, although there is no net change in reactant and product concentration over time. At equilibrium, the rates of the forward and reverse reactions are equal. Equilibrium can be established starting with only reactants, with only products, or with any mixture of reactants and products. The Equilibrium Constant rate forward = rate reverse kf[N2O4] eq = kr[NO2]2eq The subscript “eq” denotes a concentration at equilibrium. Rearranging The ratio of two constants (kf/kr) is also a constant: 15.2 equilibrium expression N2O4(g) 2NO2(g) equilibrium constant The Equilibrium Constant Note the relationship between the equilibrium constant and the balanced chemical equation: N2O4(g) 2NO2(g) The Equilibrium Constant The reaction quotient (Qc ) is a fraction with product concentrations in the numerator and reactant concentrations in the denominator. Each concentration is raised to a power equal to the corresponding stoichiometric coefficient in the balanced chemical equation. aA + bB cC + dD This law of mass action applies to not only elementary reactions, but also to more complex reactions. (at equilibrium) Worked Example 15.1 Strategy Use the law of mass action to write the equilibrium expression and plug in the equilibrium concentrations of all three species to evaluate Kc. Carbonyl chloride (COCl2), also called phosgene, is a highly poisonous gas that was used on the battlefield of World War I. It is produced by the reaction of carbon monoxide with chlorine gas: CO(g) + Cl2(g) COCl2(g) In an experiment conducted at 74°C, the equilibrium concentrations of the species involved in the reaction were as follows: [CO] = 1.2×10-2 M, [Cl2] = 0.054 M, and [COCl2] = 0.14 M. (a) Write the equilibrium expression, and (b) determine the value of the equilibrium co ... ...
