Principles of Chemistry II © Vanden BoutWhy did the color stop changing?! A.! ! the reactants were all converted into products ! B.! ! the reaction came to equilibrium! C.! ! the forward and backward reaction had the same rate! D.! ! B & C! E.! ! all of the above!Principles of Chemistry II © Vanden Bout+ H+BlueYellowWhat is changing is the ratio of the yellow form to the blue formPrinciples of Chemistry II © Vanden BoutH2O + CO H2 + CO2 At equilibrium the ratio of the molecules stops changingFigure Copyright Houghton Mifflin Company. All rights reservedPrinciples of Chemistry II © Vanden BoutFigure Copyright Houghton Mifflin Company. All rights reservedPrinciples of Chemistry II © Vanden BoutKey IdeaAt equilibrium the ratio of the products to the reactants is fixedWe'll give the ratio a nameKwe'll call it the Equilibrium Constantsince it is related to equilibria and a constantPrinciples of Chemistry II © Vanden BoutLet's look at a simple reaction between two moleculesA + B ABLet's start with 10 molecules of A10 molecules of BAAAAAAAAAABBBBBBBBBBAt equilibrium we find5 A, 5 B, and 5 ABABAABABAAABAABABBBBBPrinciples of Chemistry II © Vanden BoutABAABABAAABAABABBBBBRatio of Products to Reactants#A X # B#AB(5)x(5)5= =51Principles of Chemistry II © Vanden BoutA + B ABLet's start with 10 molecules of ABAt equilibrium we find5 A, 5 B, and 5 ABABAABABAAABAABABBBBBABABABABABABABABAB ABPrinciples of Chemistry II © Vanden BoutABAABABAAABAABABBBBBRatio of Products to Reactants#A X # B#AB(5)x(5)5= =51Same Ratio Starting from Different initial conditions!At equilibrium the ratio will always be the samePrinciples of Chemistry II © Vanden BoutLet's Look at a new conditionAABAAABAABABBBBBAABB7 A, 7B, 3 AB! A.! ! equilibrium ! B.! ! not at equilibrium!Principles of Chemistry II © Vanden BoutRatio of Products to Reactants#A X # B#AB(7)x(7)3= =493AABAAABAABABBBBBAABBNot equal to 1/5 Therefore not a equilibriumThe ratio at any given instant is called Q the reaction quotientAt equilibrium when Q = KPrinciples of Chemistry II © Vanden BoutDirection towards EquilibriumQ > K "too many" products reaction proceeds back to reactantsQ < K "too many" reactants reaction proceeds forward to productsPrinciples of Chemistry II © Vanden BoutHow do we right K for a reaction?ConcentrationsjA + kB lC +mD K = [A]j[B]kProductsReactants= [C]l[D]mPressuresKp = PAjPBkProductsReactants= PClPDmPrinciples of Chemistry II © Vanden BoutN2(g) + 3H2(g) 2NH3(g)K = [N2][H2]3ProductsReactants= [NH3]2Principles of Chemistry II © Vanden BoutHow do we know K?ΔRG° = -RT lnKΔRG° < 0 K > 1 favors productsΔRG° > 0 K < 1 favors reactantsPrinciples of Chemistry II © Vanden Bout€ lnP2P1 = −ΔHvapR1T2−1T1 ΔT = iKbmsoluteΔT = -iKfmsolutePsolvent = XsolventP°ΔP = -iXsoluteP°Π = iMRT R = 8.314 J K-1 mol-1R = 0.08206 L-atm K-1 mol-11 atm = 760
View Full Document
Unlocking...