IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

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Transcript of IB Chemistry on Dynamic Equilibrium and Equilibrium Constant

  1. 1. Dynamic EquilibriumChemical ReactionReversibleIrreversibleA COpen systemLimiting reactants used up.Reaction stopEa low, energetic/kinetic favourable -HCA CClosed system (No matter escapes)Forward rxn productsReverse rxn - reactantsProduct dissociate form reactantCReaction going onReaction stopOpen systemUnidirectionACClosed system - No matter escapeBoth direction - equilibriumACBoth forward and reverse rxn continue at equilibriumMovement of particles bet both sides goes onConc of reactants and products remain constant Rate of forward = Rate of reverse Formation and decomposition continuesTwo/more opposing rxn take place same time, same rateAt dynamic equilibriumConc remain constantVsAAPhoto: http://declanfleming.com/man-vs-escalator-equilibrium-model/http://chemistry.tutorvista.com/physical-chemistry/reversible-reaction-and-irreversibility.html
  2. 2. Dynamic EquilibriumClosed systemReversibleForward Rate, KfReverse Rate, KrLiquid -Vapour equilibrium Br2(l) Br2(g)initialequilibrium Liq and gas Br2 in dynamic equilibrium Add more liq Br2 will increase its liq mass but not conc Dynamic equilibrium, Kc bet liq and gas Br2 remain the same Macroscopic level colour/intensity liq/gas Br2 remain constant Microscopic level liq/gas Br2 equilibrium, forward/ reverse rxn going on (Rate of Vapourization = Rate of Condensation)NO change in conc liquid/vapourRate of evaporation = Rate of condensationRate of evaporation > Rate of condensationMore vapour formRate condensation increaseInitiallyBr2 (l) Br2(g)timeRateRate of condensationRate of evaporationWhy add more liq Br2 will not change intensity vapour?Remove Br2 gas - Conc Br2 gas change - affect Kc (Rate of Vapourization > Rate of Condensation)Density = Mass VolConc = Mass VolMore mass - more vol Density/conc still sameRate of vapourization/condensation depend on change in conc Br2(Rate of Vapourization = Rate of Condensation) No change in conc/intensity vapour Br2Add more Br2
  3. 3. Dynamic EquilibriumClosed systemReversibleForward Rate, KfReverse Rate, KrinitialequilibriumNO change in conc sugar solRate of dissolving = Rate of crystallizationRate of dissolving > Rate of crystallizationMore sugar dissolve - saturated sol formRate crystallization increaseInitiallytimeRateRate of crystallizationRate of dissolvingWhy add more sugar will not change sweetness/conc?Solute-solution equilibrium Sugar(s) Sugar (aq) Sugar crystals/solution in dynamic equilibrium Add sugar will not increase sugar conc/sweetness (saturated sol) Dynamic equilibrium, Kc bet sugar solid and sol remain same Macroscopic level conc/sweetness remain constant Microscopic level crystal/sol in equilibrium, forward/reverse rxn going on (Rate of Dissolving = Rate of Crystallization)Adding more water affect Kc Conc sugar changes ( Rate of Dissolving > Rate of Crystallization )Sugar (s) Sugar (aq)Add more sugarMore mass - more vol Density/conc still sameConc = Mass VolDensity = Mass VolRate of dissolving/crystallization depend on change in sugar conc(Rate of Dissolving = Rate of Crystallization) No change in sugar conc (solution)
  4. 4. Dynamic EquilibriumClosed systemReversibleForward Rate, KfReverse Rate, KrinitialequilibriumNO change in conc vapourRate of vapourization = Rate of crystallizationRate of vapourization > Rate of crystallizationMore iodine sublimeRate crystallization increaseInitiallytimeRateRate of crystallizationRate of vapourizationWhy add more I2 will not change vapour pressure/intensity?Solid-vapour equilibrium Iodine(s) Vapour(g) I2 solid/vapour in dynamic equilibrium Add more I2 will not increase vapour pressure I2 Equilibrium, Kc bet solid/vapour remain the same (Temp dependent) Macroscopic level Vapour pressure/intensity remain constant Microscopic level solid/vapour in equilibrium, forward/reverse rxn going on (Rate of Vapourization = Rate of Crystallization)Using a bigger container. Will vapour pressure change?Iodine (s) Iodine (g)Add more I2More mass - more vol Density/conc still sameConc = Mass VolDensity = Mass VolRate of vapourization/crystallization depend on change in conc I2 (Temp dependent)(Rate of Vapourization = Rate of Crystallization)Vapour pressure same
  5. 5. Dynamic EquilibriumClosed systemReversibleForward Rate, KfReverse Rate, KrLiquid -Vapour equilibrium Br2(l) Br2(g)initialequilibriumNO change in conc liquid/intensity vapour/vapour pressureRate of evaporation = Rate of condensationLiquid Br2 evaporateMacroscopic no changes2NO2(g) N2O4(g)Physical systemChemical systemVapour Br2 condenseForward rate rxn Rate CombiningBackward rate rxn Rate decompositionReversible rxn happening, same time with same rateRate of forward = Rate of backwardConc of reactants and products remain UNCHANGED not EQUALcombiningdecompositionbrowncolourless
  6. 6. Dynamic EquilibriumClosed systemReversibleForward Rate, KfReverse Rate, Kr2NO2(g) N2O4(g)Chemical systemForward rate rxn Rate CombiningBackward rate rxn Rate dissociationReversible rxn happening, same time with same rateRate of forward = Rate of backwardConc of reactant and product remain UNCHANGED/CONSTANT not EQUALcombiningdissociationConc vs timeRate vs timeConcTimeConc NO2Conc N2O4With timeConc NO2 decrease - Forward rate decrease Conc N2O4 increase - Backward rate increase 2NO2(g) N2O4(g)Forward rateBackward rateForward Rate = Backward RateConc NO2 and N2O4 remain UNCHANGED/CONSTANTbrowncolourless
  7. 7. How dynamic equilibrium is achieved in closed system?Conc of NO2 decrease over timeForward rate, Kf decrease over timeForward Rate = Reverse RateNO22NO2(g) N2O4(g)Conc of N2O4 increase over timeN2O4Reverse rate, Kr increase over timeNO2N2O412Conc of reactant/product remain constantRate3TimeConcNO2N2O4At dynamic equilibriumAs reaction proceeds concentrationAs reaction proceeds rateTime
  8. 8. Dynamic EquilibriumReversible (closed system)Forward Rate, K1 Reverse Rate, K-1Kc = ratio of molar conc of product (raised to power of their respective stoichiometry coefficient)to molar conc of reactant (raised to power of their respective stoichiometry coefficient)Conc of product and reactantat equilibriumAt EquilibriumForward rate = Backward rateConc reactants and products remainCONSTANT/UNCHANGEEquilibrium Constant KcaA(aq) + bB(aq) cC(aq) + dD(aq)coefficientSolid/liq not included in KcConc represented by [ ]K1K-1 a bc dcA BC DK 11KKKcEquilibrium Constant Kcexpress inConc vs time Rate vs timeA + BC + DConcTimeClick here notes on dynamic equilibriumExcellent NotesK1 = forward rate constantK-1 = reverse rate constant
  9. 9. Large Kc Position equilibrium shift to right More product > reactantMagnitude of Kc a bc dcA BC DK Extend of reactionHow far rxn shift to right or left?Not how fast a bc dcA BC DK Small Kc Position equilibrium shift to left More reactant > product c K c KPosition of equilibrium2CO2(g) 2CO(g) + O2(g)92 3 10 c K2H2(g) + O2(g) 2H2O(g)81 310 c KH2(g) + I2(g) 2HI(g)2 8.710 c K1Moderate Kc Position equilibrium lies slightly right Reactant and product equal amountReaction completionReactant favoured Reactant/Product equal Product favouredc KTempdependentExtendof rxnNot how fast
  10. 10. Equilibrium Constant Kc a bc dcA BC DK aA(aq) + bB(aq) cC(aq) + dD(aq)Conc of product and reactant at equilibriumEquilibrium expression HOMOGENEOUS gaseous rxn4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) N2(g) + 3H2(g) 2NH3(g)NH4CI(s) NH3(g) + HCI(g)2SO2(g) + O2(g) 2SO3(g) 5243624NH ONO H OKc 321223N HNHKc 1 13 K NH HCI c 041 13NH CINH HCIKc 122223SO OSOKc Equilibrium expression HETEROGENOUS rxnCaCO3(s) CaO(g) + CO2(g) 03121CaCOCaO COKc 121 K CaO CO c CH3COOH(l) + C2H5OH(l) CH3COOC2H5(l) + H2O(l) 12 5131213 2 5CH COOH C H OHCH COOC H H OKc Equilibrium expression HOMOGENEOUS liquid rxnCu2+(aq) + 4NH3(aq) [Cu(NH3)4]2+ 432 123 4 ( )Cu NHCu NHKcReactant/product same phaseReactant/product diff phaseSolid and liq - conc no change(not included)
  11. 11. Conc vs TimeHow dynamic equilibrium is achieved in a closed system?40 0Rate forward = breakdown = x 40 = 20Rate reverse = form = x 0 = 020 20Rate forward = breakdown = x 20 = 10Rate reverse = form = x 20 = 515 25Rate forward = breakdown = x 15 = 8Rate reverse = form = x 25 = 613 27Rate forward = breakdown = x 13 = 7Rate reverse = form = x 27 = 713 27At dynamic EquilibriumRate forward = Rate reverseBreakdown (7) = Formation (7)At dynamic EquilibriumConc reactant 13 /Product 27 constantRate vs Time1/ 41/ 2.. tan .... tan ..11 rate cons t reverserate cons t forwardK K 21327tan reac tproductKc 21/ 41/ 211 KKKc or
  12. 12. Click here to view simulationClick here simulation using paper clipsClick here simulation on reversible rxnClick here on reversible rxnSimulation on Dynamic equilibriumClick here on equilibrium constant