CHAPTER 13 AP CHEMISTRY

CHEMICAL EQUILIBRIUM Concentration of all reactants and products cease to change Concentration of all reactants and products cease to change Forward reaction A -----> B rate = k f [A] Forward reaction A -----> B rate = k f [A] Reverse reaction B -----> A rate = k r [B] Reverse reaction B -----> A rate = k r [B] Reactions are dynamic. They keep reacting, only rates are same Reactions are dynamic. They keep reacting, only rates are same Haber process to synthesis ammonia Haber process to synthesis ammonia N 2 (g) + 3H 2 (g) > 2NH 3 (g) N 2 (g) + 3H 2 (g) > 2NH 3 (g) High pressure High pressure Law of mass action Law of mass action aA + bB ----> cC + dD aA + bB ----> cC + dD k = [C] c [D] d k = equilibrium constant k = [C] c [D] d k = equilibrium constant [A] a [B] b [ ] = concentration or pressure [A] a [B] b [ ] = concentration or pressure

CONTINUE N 2 O 4 (g) -----> 2NO 2 (g) N 2 O 4 (g) -----> 2NO 2 (g) P N2O4 = 0.22 atm P NO2 = 1.56 atm P N2O4 = 0.22 atm P NO2 = 1.56 atm k = [NO 2 ] 2 = (1.56) 2 k = [NO 2 ] 2 = (1.56) 2 [N 2 O 4 ] (0.22) [N 2 O 4 ] (0.22) k = 11 atm k = 11 atm Write the equilibrium constant for the following Write the equilibrium constant for the following SO 2 (g) + 1/2O 2 (g) SO 3 SO 2 (g) + 1/2O 2 (g) SO 3 [SO 3 ] [SO 3 ] [SO 2 ][O 2 ] 1/2 [SO 2 ][O 2 ] 1/2 2NOCl(g) 2NO(g) + Cl 2 (g) 2NOCl(g) 2NO(g) + Cl 2 (g) [NO] 2 [Cl 2 ] [NO] 2 [Cl 2 ] [NOCl] 2 [NOCl] 2

MAGNITUDE OF EQUILIBRIUM CONSTANT Page 584 Page 584 Large constant states that the equilibrium lies to the right (product). Higher concentrations of product Large constant states that the equilibrium lies to the right (product). Higher concentrations of product Small constant states that the equilibrium lies to the left, favoring the reactants Small constant states that the equilibrium lies to the left, favoring the reactants The equilibrium constants for forward and reverse reactions are the reciprocals of each other k f = 1/k (k for the reverse is the reciprocal) The equilibrium constants for forward and reverse reactions are the reciprocals of each other k f = 1/k (k for the reverse is the reciprocal) Do problem on page 585 Do problem on page 585

CONTINUED k c = concentration constant k p = pressure k c = concentration constant k p = pressure k p = k c (RT) n n = change in # of moles k p = k c (RT) n n = change in # of moles Do problem on page 588 Do problem on page 588

LeCHÂTELIER PRINCIPLE If a system at equilibrium is disturbed by a change in temperature, pressure, or concentration of one of the components, the system will shift its equilibrium position so as to counteract the effect of the disturbance If a system at equilibrium is disturbed by a change in temperature, pressure, or concentration of one of the components, the system will shift its equilibrium position so as to counteract the effect of the disturbance Change in concentration Change in concentration Change in pressure Change in pressure As pressure increases equilibrium favors a decrease in moles As pressure increases equilibrium favors a decrease in moles

CONTINUED Change in temperature Change in temperature Reactant + heat product Reactant + heat product Increase temperature and the system shifts away from the heat or energy Increase temperature and the system shifts away from the heat or energy Decrease and it will shift toward it Decrease and it will shift toward it Effect of a catalyst Effect of a catalyst Changes the rate at which equilibrium is achieved (equilibrium is reached faster) but the equilibrium constant does not change Changes the rate at which equilibrium is achieved (equilibrium is reached faster) but the equilibrium constant does not change

HETEROGENEOUS EQUILIBRIA Homogeneous equilibria Homogeneous equilibria Substances are in the same phase Substances are in the same phase Heterogeneous Heterogeneous Substances are in different phases Substances are in different phases Position of equilibrium independent of pure solids and pure liquids Position of equilibrium independent of pure solids and pure liquids This means pure solids and liquids are not in the expression for k This means pure solids and liquids are not in the expression for k Water is a pure liquid so it is not expressed Water is a pure liquid so it is not expressed