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Equilibrium Graphs of A B and B A Intro to Equilibrium Tuesday January 28 2014 10 38 AM Chemical Equilibrium 14 1 14 2 A A B Reversible rxn In a Dynamic Equilibrium the rate of forward and reverse rxns are equal and no net change of concentrations occur A reaction can be product or reactant favored depending on where the concentrations lie at equilibrium Note Equilibrium can also be viewed and expressed in terms of pressure In such a case Kp will be used instead of Kc and partial pressures replaces conc 2 3 The Equilibrium Constant K 14 3 The Equilibrium constant K is a number that determines whether a reversible rxn is product favored or reactant favored Considering the following reaction aA bB cC dD If z 1 rxn is Product Favored If z 1 rxn is Reactant Favored If z 1 rxn favors neither Pure solvents or solids are assigned a concentration value of 1 Relationship between Chemical Equation and K 1 Rxn Reversals a b c Reversing the reaction will yield and inverse value of Kold Example A 2B 3C can be reversed as 3C 2B A Knew 1 Kold Rxn Factors a Multiplying or dividing the rxn coefficients by value n n b Knew Kold c Example A 2B 3C becomes 2A 4B 6C where n 2 Adding Rxns Together a When adding rxns together Knew K1 K2 K3 b Example 1 A 2B K 1 2 2B 3C K 3 3 A 3C K 1 3 3 1 2 3 4 1 2 3 4 Example with all relationships H2 g Br2 g 2HBr g K1 7 9x1011 25C H2 g 2H g K2 4 8x10 41 25C Br2 g 2Br g K3 2 2x10 15 25C H g Br g HBr g KT To solve for target equations K value rearrange equations to match target equations 1 2H2 g 1 2Br2 HBr g K1new K1old H g 1 2H2 g K2new K2old Br g 1 2Br2 g K3new K3old H g Br g HBr g KT K1new K2new K3new 2 7x1033 25C 1 2 1 1 2 1 1 2 Reaction Quotient Q 14 7 A reaction quotient looks similar to the K equation but instead of using Equilibrium concentration it utilizes any other concentration to determine if the system is at has passed or has not yet reached equilibrium Can be expressed in terms of concentration OR pressure If Q K Equilibrium has been passed If Q K The system is in Equilibrium If Q K Equilibrium has not been reached Initial Current Equilibrium or ICE To find concentrations at equilibrium use an ICE chart CO g 2H2 g CH3OH g COi 500M H2i 1 00M COf 15 M CH3OH g CO g H2 g 500 1 00 0 I C E 0 350 0 70 0 350 150 300 0 350 Fill in known values and solve for missing information Chem Page 1

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