Principles of Chemistry II © Vanden BoutChemical EquilibriaWhy do we care?!!Principles of Chemistry II © Vanden BoutPut stuff in a beaker and what do you get?We can use thermodynamics to predict the molecular concentrations at equilibrium(very powerful!)2H2O(g) 2H2(g) + O2(g)ΔrG° = +113.4 kJ mol-1Principles of Chemistry II © Vanden BoutWhat about the opposite reaction?2H2(g) + O2(g) 2H2O(g) ΔrG° = -113.4 kJ mol-1Principles of Chemistry II © Vanden BoutDoes everything go to equilibrium as predicted?What happens if you mix H2 and O2 at 298K?! A.! ! The explode and form water! B.! ! They explode and form hydrogen peroxide (H2O2) ! C.! ! NothingPrinciples of Chemistry II © Vanden BoutWhy didn’t I get to equilibrium?Kinetics Other ReactionsPrinciples of Chemistry II © Vanden BoutChemical EquilibriaWhy do we care?!!Things might not get to equilibriumbut they never move away from itPrinciples of Chemistry II © Vanden BoutWhy does K depend on ΔrG°?A BimagineΔrG° = 0GReactionPrinciples of Chemistry II © Vanden BoutA BimagineΔrG° = 0GReactionPrinciples of Chemistry II © Vanden BoutA BimagineΔrG° > 0GReactionPrinciples of Chemistry II © Vanden BoutFigure Copyright Houghton Mifflin Company. All rights reservedEquilibrium does not depend on starting conditionsEach equilibrium has different concentrations, but the same value for KcPrinciples of Chemistry II © Vanden BoutA convention to keep things straightwe’ll be doing a lot of aqueous problemsC denote concentrations initially[ ] denote concentrations at equilibrium3H2(g) + N2(g) 2NH3(g)ReactionInitialChangeEquilibriumPrinciples of Chemistry II © Vanden Bout3H2(g) + N2(g) 2NH3(g)ReactionInitialChangeEquilibriumReally Easy problemsAt equilibrium you find[H2] = .1 M, [N2] = 0.2 M, and [NH3] = .2MK =Principles of Chemistry II © Vanden Bout3H2(g) + N2(g) 2NH3(g)ReactionInitialChangeEquilibriumFairly Easy problemGiven K = 200 and [H2] = .2 M, [N2] = 0.4 M, and CNH3 = .1Mfill in the restPrinciples of Chemistry II © Vanden Bout3H2(g) + N2(g) 2NH3(g)ReactionInitialChangeEquilibriumTypical problemGiven K = 200 and CH2 = .2 M, N2 = 0.2 M what are theconcentrations at equilibriumPrinciples of Chemistry II © Vanden Bout3H2(g) + N2(g) 2NH3(g)ReactionInitialChangeEquilibrium.2 .2 0-3x -x +2x.2-3x .2-x +2xPrinciples of Chemistry II © Vanden BoutI thought you said we need to use Kp for gasesand Kc for solutions?Principles of Chemistry II © Vanden BoutRelating Kp and Kc2NO2(g) N2O4(g)Kc =Kp =PN2O4 =Principles of Chemistry II © Vanden BoutRelating Kp and Kc2NO2(g) N2O4(g)Kp =PN2O4PNO22=[N2O4]RT[NO2]2(RT)2=In general KP = Kc(RT)ΔnΔn is the change in the number of moles of gasPrinciples of Chemistry II © Vanden BoutTime out for activitiesThat is what we are actually putting into the equilibrium constantGasai = Compoundin solutionai = Free Energy Changes with PFree Energy Changes with ConcentrationPrinciples of Chemistry II © Vanden BoutWhat about the activity of a pure liquid or solid?ai = The pure compound is the reference state!Pure solids and liquids “don’t show up”in the equilibrium constant(they are there. they are just always = 1)Principles of Chemistry II © Vanden BoutWhat is the equilibrium constant for this reaction?H2O(l) H2O(g) K =Principles of Chemistry II © Vanden BoutEquilibria with more than one phaseare called Heterogeneous EquilibriaCaCO3(s) CaO(s) + CO2(g)K=Principles of Chemistry II © Vanden BoutFor the following reaction ΔRG° = +740 kJ mol-1 at 298KIn air will I form any solid iron?Fe2O3(s) 2Fe(s) + (3/2)O2(g)! A.! ! all the iron oxide will convert to iron ! B.! ! about half of the iron oxide will convert to iron! C.! ! a very small amount of the iron oxide will convert to iron! D.! ! not a single atom of iron will formPrinciples of Chemistry II © Vanden BoutFor the following reaction ΔRG° = +740 kJ mol-1 at 298KIn air will I form any solid iron?Fe2O3(s) 2Fe(s) + (3/2)O2(g)What is Q?K= exp[-740,000/(8.314)(298)] = 2 x 10-130Principles of Chemistry II © Vanden BoutWhat is equilibrium good for?Drug + Protein Drug-Protein ComplexFendrick et al. Osteopathic Medicine and Primary Care 2008 2:2 doi:10.1186/1750-4732-2-2Principles of Chemistry II © Vanden BoutDrug BindingHow “strongly” should it bind to work?Drug + Protein Drug-Protein ComplexK = Do an experiment Measure KPrinciples of Chemistry II © Vanden BoutFor ibuprofin binding to the COX channel K ~ 108Drug + Protein Drug-Protein ComplexIf we want 100x more complexed protein than free proteinwhat concentration of drug do we need?! A.! ! 10-8 M ! B.! ! 10-6 M! C.! ! 10-4 M! D.! ! 10-2 MK = [complex][drug][protein]Principles of Chemistry II
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