7.2 Equilibrium Law and the Equilibrium Constant.pptx - Equilibrium Law and the Equilibrium Constant Chapter 7.2 • Equilibrium law is the mathematical

7.2 Equilibrium Law and the Equilibrium Constant.pptx -...

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Unformatted text preview: Equilibrium Law and the Equilibrium Constant Chapter 7.2 • Equilibrium law is the mathematical description of a chemical system at equilibrium • The equilibrium constant (K) is the numerical value defining the equilibrium law fora given system K is a unitless quantity K is constant for a given reaction at a given temperature Example: 4NH3 (g) + 7O2 (g) 4NO2 (g) + 6H2O (g) The equation must be correctly balanced 4 6 NO2 H2 O Keq 4 7 NH3 O2 Practice • Write equilibrium law equations for these reactions: a) 2O3 (g) 3O2 (g) b) H2 (g) + F2 (g) 2HF(g) Results for three experiments for the reaction: 2NH3 (g) at 500 C N2 (g) + 3H2 (g) expt Initial Concentrations Equilibrium Concentrations [ NH 3 ]2 K [ N 2 ] [ H 2 ]3 [N2] [H2] [NH3] [N2] [H2] [NH3] I 1.000 1.000 0 0.921 0.763 0.157 0.0602 II 0 0 1.00 0.399 1.197 0.203 0.0602 III 2.00 1.00 3.00 2.59 2.77 1.82 0.0602 N2O4(g) ↔ 2NO2(g) The Equilibrium Constant Varies with Temperature Practice 4SO2 (g) + O2 (g) 2SO3(g) Experiment 1 Initial Equilibrium [SO2 ] = 2.00M [SO2 ] = 1.50M [O2 ] = 1.50M [O2 ] = 1.25M [SO3 ] = 3.00M [SO3] = 3.50M Equilibrium constant for Experiment 1 = Experiment 2 Initial Equilibrium [SO2 ] = 0.500M [SO2 ] = 0.590M [O2 ] = 0.00M [O2 ] = 0.045M [SO2 ] = 0.350M [SO3 ] = 0.260M Equilibrium constant for Experiment 2 = Heterogeneous Equilibria • A heterogeneous equilibrium system is one in which the reactants and products are present in at least two different states, such as gases and solids • If pure solids or pure liquids are involved in a chemical equilibrium system, their concentrations are not included in the equilibrium law equation for the reaction system CaCO3 (s) CO2 (g) + Calcium carbonate carbon dioxide CaO(s) lime Practice • Write equilibrium law equations for these reactions: a) H2 (g) + O2 (g) b) NH4Cl (s) H2O (l) NH3 (g) + HCl(g) The Magnitude of K • The magnitude of the equilibrium constant, K, tells us whether the equilibrium position favours products or reactants If K=1 If K>1 If K<1 K(forward) and K(reverse) 2O3(g) 3O2(g) HOMEWORK Required Reading: p. 429-436 (remember to supplement your notes!) Questions: p. 431 #1-3 p. 434 #1 p. 436 #1-6 ...
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  • Fall '13
  • Longsworth
  • Chemical reaction, Equilibrium Law, NO2  H2

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