CHAPTER 13CHAPTER 13

AP CHEMISTRYAP CHEMISTRY

CHEMICAL EQUILIBRIUMCHEMICAL EQUILIBRIUM Concentration of all reactants and products cease Concentration of all reactants and products cease

to changeto change Forward reaction A -----> B Forward reaction A -----> B rate = krate = kff[A][A] Reverse reaction B -----> A Reverse reaction B -----> A raterate = k = krr[B][B] Reactions are dynamic. They keep reacting, only Reactions are dynamic. They keep reacting, only

rates are samerates are same Haber process to synthesis ammoniaHaber process to synthesis ammonia NN22(g) + 3H(g) + 3H22(g) ------------------> 2NH(g) ------------------> 2NH33(g)(g) High pressureHigh pressure Law of mass actionLaw of mass action aA + bB ----> cC + dDaA + bB ----> cC + dD k = k = [C][C]cc [D] [D]dd k = equilibrium constantk = equilibrium constant [A][A]aa [B] [B]bb [ ] = concentration or pressure[ ] = concentration or pressure

CONTINUECONTINUE NN22OO44(g) -----> 2NO(g) -----> 2NO22(g)(g) PPN2O4N2O4 = 0.22 atm P = 0.22 atm PNO2NO2 = 1.56 atm = 1.56 atm k = k = [NO[NO22]]22 = = (1.56)(1.56)22 [N[N22OO44] (0.22)] (0.22) k = 11 atmk = 11 atm Write the equilibrium constant for the followingWrite the equilibrium constant for the following SOSO22(g) + 1/2O(g) + 1/2O22(g) <------> SO(g) <------> SO33 [SO[SO33 ] ] [SO[SO22][O][O22]]1/21/2

2NOCl(g) <=====> 2NO(g) + Cl2NOCl(g) <=====> 2NO(g) + Cl22(g)(g) [NO][NO]22[Cl[Cl22]] [NOCl][NOCl]22

MAGNITUDE OF EQUILIBRIUM MAGNITUDE OF EQUILIBRIUM CONSTANTCONSTANT

Page 584Page 584 Large constant states that the equilibrium lies to Large constant states that the equilibrium lies to

the right (product). Higher concentrations of the right (product). Higher concentrations of productproduct

Small constant states that the equilibrium lies to Small constant states that the equilibrium lies to the left, favoring the reactantsthe left, favoring the reactants

The equilibrium constants for forward and The equilibrium constants for forward and reverse reactions are the reciprocals of each reverse reactions are the reciprocals of each other kother kff = 1/k (k for the reverse is the reciprocal) = 1/k (k for the reverse is the reciprocal)

Do problem on page 585Do problem on page 585

CONTINUEDCONTINUED

kkcc = concentration constant k = concentration constant kpp = pressure = pressure

kkpp = k = kcc(RT)(RT)nn n = change in # of moles n = change in # of moles Do problem on page 588Do problem on page 588

LeCHÂTELIER PRINCIPLELeCHÂTELIER PRINCIPLE If a system at equilibrium is disturbed by a If a system at equilibrium is disturbed by a

change in temperature, pressure, or change in temperature, pressure, or concentration of one of the components, concentration of one of the components, the system will shift its equilibrium position the system will shift its equilibrium position so as to counteract the effect of the so as to counteract the effect of the disturbancedisturbanceChange in concentrationChange in concentration

Change in pressureChange in pressureAs pressure increases equilibrium favors a As pressure increases equilibrium favors a

decrease in molesdecrease in moles

CONTINUEDCONTINUED

Change in temperatureChange in temperature Reactant + heat <====> productReactant + heat <====> product Increase temperature and the system shifts Increase temperature and the system shifts

away from the heat or energyaway from the heat or energy Decrease and it will shift toward itDecrease and it will shift toward it Effect of a catalystEffect of a catalyst Changes the rate at which equilibrium is Changes the rate at which equilibrium is

achieved (equilibrium is reached faster) but the achieved (equilibrium is reached faster) but the equilibrium constant does not change equilibrium constant does not change

HETEROGENEOUS EQUILIBRIAHETEROGENEOUS EQUILIBRIA

Homogeneous equilibriaHomogeneous equilibria Substances are in the same phaseSubstances are in the same phase

HeterogeneousHeterogeneous Substances are in different phasesSubstances are in different phases

Position of equilibrium independent of pure Position of equilibrium independent of pure solids and pure liquidssolids and pure liquids

This means pure solids and liquids are not in the This means pure solids and liquids are not in the expression for kexpression for k

Water is a pure liquid so it is not expressedWater is a pure liquid so it is not expressed