Chemical Equilibriumq

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Chemical Equilibriumq. Reaction Dynamics. when a reaction starts, the reactants are consumed and products are made forward reaction = reactants  products therefore the reactant concentrations decrease and the product concentrations increase - PowerPoint PPT Presentation

Transcript of Chemical Equilibriumq

  • ChemicalEquilibriumq

  • Reaction Dynamicswhen a reaction starts, the reactants are consumed and products are madeforward reaction = reactants productstherefore the reactant concentrations decrease and the product concentrations increaseas reactant concentration decreases, the forward reaction rate decreaseseventually, the products can react to reform some of the reactantsreverse reaction = products reactantsassuming the products are not allowed to escapeas product concentration increases, the reverse reaction rate increasesprocesses that proceed in both the forward and reverse direction are said to be reversiblereactants products

  • Hypothetical Reaction2 Red BlueThe reaction slows over time,But the Red molecules never run out!At some time between 100 and 110 sec,the concentrations of both the Red andthe Blue molecules no longer change equilibrium has been established.Notice that equilibrium does not meanthat the concentrations are equal!Once equilibrium is established, the rateof Red molecules turning into Blue is thesame as the rate of Blue molecules turning into Red

    Time[Red][Blue]00.4000.000100.2080.096200.1900.105300.1800.110400.1740.113500.1700.115600.1680.116700.1670.117800.1660.117900.1650.1181000.1650.1181100.1640.1181200.1640.1181300.1640.1181400.1640.1181500.1640.118

  • Hypothetical Reaction2 Red Blue

    Sheet1

    Choose the reaction you wish to investigate

    Choose the Initial Concentration of Chemicals[A]init =[Y]init =

    00

    Choose the Celsius temperature you wish to useChoose the time interval between readings

    Choose the value of DG, in Joules

    Choose the order for each reactant in the forward rate equationOrder of A =0

    Choose the order for each product in the reverse rate equationOrder of Y =0

    Choose the activation energy, in joules, for the forward reaction

    Given the above information, the equilibrium constant, K, for the reaction will equal3.2

    Given the above information, the value of the forward reaction rate constant, kf, will equal0.15

    Given the above information, the value of the reverse reaction rate constant, kr, will equal0.0475

    Data Sheet

    Reaction ListCoeff ACoeff BCoeff YCoeff ZCoeffA =2Init Conc[A]init =0.4OrdersA order =2

    2 A ----> YA ----> Y1010CoeffB =00.1[B]init =0.10B order =1

    2 A ----> Y2010CoeffY =10.2[Y]init =01Y order =1

    A ----> 2 Y1020CoeffZ =00.3[Z]init =0.42Z order =0

    3 A ----> Y30100.4

    A ----> 3 Y10300.5

    2 A ----> 3 Y20300.6

    3 A ----> 2 Y30200.7

    A + B ----> Y11100.8

    2 A + B ----> Y21100.9

    A + B ----> 2 Y11201

    A + B ----> Y + Z1111

    2 A + B ----> Y + Z2111

    A + B ----> 2 Y + Z1121

    Time IntervalTime Interval List, secondsTotal Time

    20.550

    1100

    2200

    5500

    101000

    Temp, CTemp List, CTemp, K

    250-100523

    0

    50R, J/mol-K

    1008.314

    500

    DGDG List, JKx

    -5000-250003.2E+000

    -20000Kcalc

    -150003.1578622343

    -10000

    -5000

    0

    5000

    10000

    15000

    20000

    25000

    Ea forwardEa List, jouleskfkf_calcForward Collision Freq, Afkf/kr

    700010001.50E-010.14993768880.753.1578947368

    3000

    Ea reverse5000krkr_calcReverse Collision Freq, Ar

    1200070004.75E-020.04748075680.75

    10000

    Calc Sheet

    Mole MultiplierAvog. Number

    1.66E-196.02E+23

    Time[Red]0[Blue]0Molecules AMolecules BMolecules YMolecules ZRate ForwardRate ReverseMolecules A ReactMolecules B ReactMolecules Y ReactMolecules Z ReactMolecules A MadeMolecules B MadeMolecules Y MadeMolecules Z Made

    00.4000400000000.024038400000019200

    20.361725880600.01920668390361600192000.01962684190.000912317528390408014200

    40.333406025300.03337161330333290333600.01667393670.00158515162223011022011120

    60.311388363200.04438544610311280443700.01454440690.0021083087181101903809060

    80.29365219100.0532585340293550532400.01293474140.0025297804151902705407600

    100.27899709100.06059108570278900605700.01167590650.0028780766130303507006520

    120.266662798700.06676323360266570667400.01066635720.0031712536113704208405690

    140.256129132900.07203506820256040720100.00984031990.0034216657100804909805040

    160.24702596500.07658665220246940765600.00915327410.003637866904056011204520

    180.239103207900.08054803070239020805200.00857555160.0038260315820062012404100

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    220.225978640600.08711031440225900870800.00765995190.0041377399692072014403460

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    280.211213502300.0945028870211140944700.00669167150.0044888871565085017002830

    300.207262127200.09648357630207190964500.00644363840.0045829699534088017602670

    320.203680880900.09827419940203610982400.00622288520.0046680245507092018402540

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    3520.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3540.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3560.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3580.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3600.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3620.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3640.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3660.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3680.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3700.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3720.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3740.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3760.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3780.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3800.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3820.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3840.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3860.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3880.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3900.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3920.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3940.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3960.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    3980.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    4000.164377203300.118121106101643201180800.00405297970.00561075252660133026601330

    Conc vs Time

    0.40

    0.36172588060.0192066839

    0.33340602530.0333716133

    0.31138836320.0443854461

    0.2936521910.053258534

    0.2789970910.0605910857

    0.26666279870.0667632336

    0.25612913290.0720350682

    0.2470259650.0765866522

    0.23910320790.0805480307

    0.2321407850.0840292422

    0.22597864060.0871103144

    0.22049673290.0898512682

    0.21560503060.0923021211

    0.21121350230.094502887

    0.20726212720.0964835763

    0.20368088090.0982741994

    0.20044975650.0998947634

    0.19751873650.1013652751

    0.19485781050.1026957381

    0.19241696110.1039161628

    0.19020619180.1050265492

    0.18817548510.1060469043

    0.18631483760.1069772281

    0.18461424580.107827524

    0.18304369920.108617799

    0.18160319790.1093380496

    0.18029274190.1099982794

    0.17907231720.1106084918

    0.17795192730.1111686867

    0.17691156520.1116888677

    0.1759512310.1121690348

    0.17506092120.1126191915

    0.17424063570.1130293342

    0.17349037470.1134094665

    0.17280013440.1137595883

    0.17216991510.1140796997

    0.17158971320.1143698007

    0.17103952180.1146498982

    0.17053934770.1148999852

    0.17006918410.1151400687

    0.16963903440.1153601453

    0.16922889170.1155702184

    0.16885876280.1157602846

    0.1685086410.1159403472

    0.16819853310.1161004029

    0.16790843210.1162504552

    0.16762833470.1163905039

    0.16737824760.1165205492

    0.16714816760.1166405909

    0.1669280910.1167506292

    0.16671801790.1168606675

    0.16653795520.1169506988

    0.1663678960.1170407302

    0.16620784030.117120758

    0.16605778810.1172007859

    0.16590773590.1172808137

    0.16578769410.1173408346

    0.16567765580.1174008555

    0.16556761750.1174608764

    0.16546758270.1175108938

    0.16536754790.1175609112

    0.16527751660.1176109286

    0.16518748520.117660946

    0.16510745740.1177009599

    0.16504743650.1177309704

    0.16498741560.1177609808

    0.16493739820.1177909913

    0.16488738080.1178210017

    0.16483736340.1178510122

    0.1647873460.1178810226

    0.16474733210.1179010296

    0.16470731810.1179210365

    0.16466730420.1179410435

    0.16462729030.1179610504

    0.16458727640.1179810574

    0.16455726590.1180010644

    0.16452725550.1180210713

    0.1644972450.1180410783

    0.16446723460.1180610853

    0.16443722420.1180810922

    0.16440721370.1181010992

    0.16437720330.1181211061

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    [Red]

    [Blue]

    Time, sec

    Concentration

    Concentration vs. Time for 2 Red --> Blue

    MBD00000100.unknown

    MBD00000240.unknown

    MBD000002E0.unknown

    MBD00000380.unknown

    MBD000003D0.unknown

    MBD0057AC9A.unknown

    MBD005704B5.unknown

    MBD000003CC.unknown

    MBD00000330.unknown

    MBD0000037C.unknown

    MBD0000032C.unknown

    MBD00000290.unknown

    MBD000002DC.unknown

    MBD0000028C.unknown

    MBD000001A0.unknown

    MBD000001F0.unknown

    MBD0000023C.unknown

    MBD000001EC.unknown

    MBD00000150.unknown

    MBD0000019C.unknown

    MBD0000014C.unknown

    MBD000000A4.unknown

    MBD000000FC.unknown

    MBD00000050.unknown

  • Reaction DynamicsTimeRateInitially, only the forwardreaction takes place.As the forward reaction proceedsit makes products and uses reactants.Because the reactant concentration decreases, the forward reaction slows.As the products accumulate, thereverse reaction speeds up.Eventually, the reaction proceedsin the reverse direction as fast asit proceeds in the forward direction.At this time equilibrium is established.Once equilibrium is established,the forward and reverse reactions proceed at the same rate, so theconcentrations of all materialsstay constant.

  • Dynamic Equilibriumas the forward reaction slows and the reverse reaction accelerates, eventually they reach the same ratedynamic equilibrium is the condition where the rates of the forward and reverse reactions are equalonce the reaction reaches equilibrium, the concentrations of all the chemicals remain constantbecause the chemicals are being consumed and made at the same rate

  • H2(g) + I2(g) 2 HI(g)at time 0, there are only reactants in the mixture, so only the forward reaction can take place[H2] = 8, [I2] = 8, [HI] = 0at time 16, there are both reactants and products in the mixture, so both the forward reaction and reverse reaction can take place [H2] = 6, [I2] = 6, [HI] = 4

  • H2(g) + I2(g) 2 HI(g)at time 32, there are now more products than reactants in the mixture the forward reaction has slowed down as the reactants run out, and the reverse reaction accelerated[H2] = 4, [I2] = 4, [HI] = 8at time 48, the amounts of products and reactants in the mixture havent changed the forward and reverse reactions are proceeding at the same rate it has reached equilibrium

  • H2(g) + I2(g) 2 HI(g)Since the [HI] at equilibrium is larger than the [H2] or [I2], we say the position of equilibrium favors productsAs the reaction proceeds, the [H2] and [I2] decrease and the [HI] increasesSince the reactant concentrations are decreasing, the forward reaction rate slows downAnd since the product concentration is increasing, the reverse reaction rate speeds upOnce equilibrium is established, the concentrations no longer changeAt equilibrium, the forward reaction rate is the same as the reverse reaction rate

  • Equilibrium Equalthe rates of the forward and reverse reactions are equal at equilibriumbut that does not mean the concentrations of reactants and products are equalsome reactions reach equilibrium only after almost all the reactant molecules are consumed we say the position of equilibrium favors the productsother reactions reach equilibrium when only a small percentage of the reactant molecules are consumed we say the position of equilibrium favors the reactants

  • An Analogy: Population Changes

  • Equilibrium Constanteven though the concentrations of reactants and products are not equal at equilibrium, there is a relationship between themthe relationship between the chemical equation and the concentrations of reactants and products is called the Law of Mass Action for the general equation aA + bB cC + dD, the Law of Mass Action gives the relationship below the lowercase letters represent the coefficients of the balanced chemical equationalways products over reactants K is called the equilibrium constantunitless

  • Writing Equilibrium Constant Expressionsfor the reaction aA(aq) + bB(aq) cC(aq) + dD(aq) the equilibrium constant expression is so for the reaction 2 N2O5 4 NO2 + O2 the equilibrium constant expression is:

  • What Does the Value of Keq Imply? when the value of Keq >> 1, we know that when the reaction reaches equilibrium there will be many more product molecules present than reactant moleculesthe position of equilibrium favors productswhen the value of Keq
  • A Large Equilibrium Constant

  • A Small Equilibrium Constant

  • Relationships between K and Chemical Equationswhen the reaction is written backwards, the equilibrium constant is invertedfor the reaction aA + bB cC + dDthe equilibrium constant expression is:for the reaction cC + dD aA + bBthe equilibrium constant expression is:

  • Relationships between K and Chemical Equationswhen the coefficients of an equation are multiplied by a factor, the equilibrium constant is raised to that factorfor the reaction aA + bB cC the equilibrium constant expression is:for the reaction 2aA + 2bB 2cC the equilibrium constant expression is:

  • Relationships between K and Chemical Equationswhen you add equations to get a new equation, the equilibrium constant of the new equation is the product of the equilibrium constants of the old equationsfor the reactions (1) aA bB and (2) bB cC the equilibrium constant expressions are:for the reaction aA cC the equilibrium constant expression is:

  • Kbackward = 1/Kforward, Knew = KoldnCompute the equilibrium constant at 25C for the reaction NH3(g) 0.5 N2(g) + 1.5 H2(g) for N2(g) + 3 H2(g) 2 NH3(g), K = 3.7 x 108 at 25C

    K for NH3(g) 0.5N2(g) + 1.5H2(g), at 25C Solution:Concept Plan:

    Relationships:Given:

    Find:N2(g) + 3 H2(g) 2 NH3(g)K1 = 3.7 x 1082 NH3(g) N2(g) + 3 H2(g) NH3(g) 0.5 N2(g) + 1.5 H2(g)

  • Equilibrium Constants for Reactions Involving Gasesthe concentration of a gas in a mixture is proportional to its partial pressuretherefore, the equilibrium constant can be expressed as the ratio of the partial pressures of the gasesfor aA(g) + bB(g) cC(g) + dD(g) the equilibrium constant expressions areor

  • Kc and Kpin calculating Kp, the partial pressures are always in atmthe values of Kp and Kc are not necessarily the samebecause of the difference in unitsKp = Kc when Dn = 0the relationship between them is:Dn is the difference between the number of moles of reactants and moles of products

  • Deriving the Relationshipbetween Kp and KcKonsentrasi nitrogen 75% = misal terdapat 100 mol gas yang ada dalam udara, 75 mol merupakan gas nitrogen dalam udara, 25 molMerupakan gas h dan o

    % volum merupakan Banyaknya volume gas dalam volum gas total

  • Deriving the RelationshipBetween Kp and Kcfor aA(g) + bB(g) cC(g) + dD(g)substituting

  • Find Kc for the reaction 2 NO(g) + O2(g) 2 NO2(g), given Kp = 2.2 x 1012 @ 25CK is a unitless numbersince there are more moles of reactant than product, Kc should be larger than Kp, and it isKp = 2.2 x 1012Kc Check:Solution:Concept Plan:

    Relationships:Given:

    Find:2 NO(g) + O2(g) 2 NO2(g)Dn = 2 3 = -1

  • Heterogeneous Equilibriapure solids and pure liquids are materials whose concentration doesnt change during the course of a reactionits amount can change, but the amount of it in solution doesnt because it isnt in solutionbecause their concentration doesnt change, solids and liquids are not included in the equilibrium constant expressionfor the reaction aA(s) + bB(aq) cC(l) + dD(aq) the equilibrium constant expression is:

  • Heterogeneous EquilibriaThe amount of C is different, but the amounts of CO and CO2 remains the same. Therefore the amount of C has no effect on the position of equilibrium.

  • Calculating Equilibrium Constants from Measured Equilibrium Concentrationsthe most direct way of finding the equilibrium constant is to measure the amounts of reactants and products in a mixture at equilibriumactually, you only need to measure one amount then use stoichiometry to calculate the other amountsthe equilibrium mixture may have different amounts of reactants and products, but the value of the equilibrium constant will always be the sameas long as the temperature is kept constantthe value of the equilibrium constant is independent of the initial amounts of reactants and products

  • Initial and Equilibrium Concentrations forH2(g) + I2(g) 2HI(g) @ 445C

    InitialEquilibriumEquilibriumConstant[H2][I2][HI][H2][I2][HI]0.500.500.00.110.110.780.00.00.500.0550.0550.390.500.500.500.1650.1651.171.00.50.00.530.0330.934

  • Calculating Equilibrium ConcentrationsStoichiometry can be used to determine the equilibrium concentrations of all reactants and products if you know initial concentrations and one equilibrium concentrationsuppose you have a reaction 2 A(aq) + B(aq) 4 C(aq) with initial concentrations [A] = 1.00 M, [B] = 1.00 M, and [C] = 0. You then measure the equilibrium concentration of C as [C] = 0.50 M.+0.50-(0.50) -(0.50) 0.750.88

    [A][B][C]initial molarity1.001.000change in concentrationequilibrium molarity0.50

  • Find the value of Kc for the reaction2 CH4(g) C2H2(g) + 3 H2(g) at 1700C if the initial [CH4] = 0.115 M and the equilibrium [C2H2] = 0.035 M+0.035

    Construct an ICE table for the reactionfor the substance whose equilibrium concentration is known, calculate the change in concentration

    [CH4][C2H2][H2]initial0.1150.0000.000changeequilibrium0.035

  • Find the value of Kc for the reaction2 CH4(g) C2H2(g) + 3 H2(g) at 1700C if the initial [CH4] = 0.115 M and the equilibrium [C2H2] = 0.035 M+0.035-2(0.035) +3(0.035) 0.0450.105

    use the known change to determine the change in the other materialsadd the change to the initial concentration to get the equilibrium concentration in each columnuse the equilibrium concentrations to calculate Kc

    [CH4][C2H2][H2]initial0.1150.0000.000changeequilibrium0.035

  • The following data were collected for the reaction 2 NO2(g) N2O4(g) at 100C. Complete the table and determine values of Kp and Kc for each experiment.

    Expt 1

    Expt 2

    initial [N2O4]

    0

    0.0200

    initial [NO2]

    0.0200

    0

    change [N2O4]

    change [NO2]

    equilibrium [N2O4]

    0.00452

    equilibrium [NO2]

    0.0172

  • The following data were collected for the reaction 2 NO2(g) N2O4(g) at 100C. Complete the table and determine values of Kp and Kc for each experiment.

    Expt 1

    Expt 2

    initial [N2O4]

    0

    0.0200

    initial [NO2]

    0.0200

    0

    change [N2O4]

    +0.0014

    -0.0155

    change [NO2]

    -0.0028

    +0.0310

    equilibrium [N2O4]

    0.0014

    0.00452

    equilibrium [NO2]

    0.0172

    0.0310

  • The Reaction Quotientif a reaction mixture, containing both reactants and products, is not at equilibrium; how can we determine which direction it will proceed?the answer is to compare the current concentration ratios to the equilibrium constantthe concentration ratio of the products (raised to the power of their coefficients) to the reactants (raised to the power of their coefficients) is called the reaction quotient, Q for the gas phase reactionaA + bB cC + dDthe reaction quotient is:

  • The Reaction Quotient:Predicting the Direction of Changeif Q > K, the reaction will proceed fastest in the reverse directionthe [products] will decrease and [reactants] will increaseif Q < K, the reaction will proceed fastest in the forward directionthe [products] will increase and [reactants] will decreaseif Q = K, the reaction is at equilibriumthe [products] and [reactants] will not changeif a reaction mixture contains just reactants, Q = 0, and the reaction will proceed in the forward directionif a reaction mixture contains just products, Q = , and the reaction will proceed in the reverse direction

  • Q, K, and the Direction of Reaction

  • If Q = K, equilibrium; If Q < K, forward; If Q > K, reverseFor the reaction below, which direction will it proceed if PI2 = 0.114 atm, PCl2 = 0.102 atm & PICl = 0.355 atm for I2(g) + Cl2(g) 2 ICl(g), Kp = 81.9

    direction reaction will proceed Solution:Concept Plan:

    Relationships:Given:

    Find:I2(g) + Cl2(g) 2 ICl(g)Kp = 81.9since Q (10.8) < K (81.9), the reaction will proceed to the right

  • If [COF2]eq = 0.255 M and [CF4]eq = 0.118 M, and Kc = 2.00 @ 1000C, find the [CO2]eq for the reaction given.Units & Magnitude OKCheck:Check: Round to 1 sig fig and substitute back inSolution:Solve: Solve the equilibrium constant expression for the unknown quantity by substituting in the given amountsConcept Plan:

    Relationships:Strategize: You can calculate the missing concentration by using the equilibrium constant expression2 COF2 CO2 + CF4[COF2]eq = 0.255 M, [CF4]eq = 0.118 M [CO2]eqGiven:

    Find:Sort: Youre given the reaction and Kc. Youre also given the [X]eq of all but one of the chemicals

  • A sample of PCl5(g) is placed in a 0.500 L container and heated to 160C. The PCl5 is decomposed into PCl3(g) and Cl2(g). At equilibrium, 0.203 moles of PCl3 and Cl2 are formed. Determine the equilibrium concentration of PCl5 if Kc = 0.0635

  • A sample of PCl5(g) is placed in a 0.500 L container and heated to 160C. The PCl5 is decomposed into PCl3(g) and Cl2(g). At equilibrium, 0.203 moles of PCl3 and Cl2 are formed. Determine the equilibrium concentration of PCl5 if Kc = 0.0635PCl5 PCl3 + Cl2

    equilibriumconcentration, M?

  • Finding Equilibrium Concentrations When Given the Equilibrium Constant and Initial Concentrations or Pressuresfirst decide which direction the reaction will proceedcompare Q to Kdefine the changes of all materials in terms of xuse the coefficient from the chemical equation for the coefficient of xthe x change is + for materials on the side the reaction is proceeding towardthe x change is for materials on the side the reaction is proceeding away fromsolve for xfor 2nd order equations, take square roots of both sides or use the quadratic formulamay be able to simplify and approximate answer for very large or small equilibrium constants

  • For the reaction I2(g) + Cl2(g) 2 ICl(g) @ 25C, Kp = 81.9. If the initial partial pressures are all 0.100 atm, find the equilibrium concentrations since Qp(1) < Kp(81.9), the reaction is proceeding forward

    [I2][Cl2][ICl]initial0.1000.1000.100changeequilibrium

    Construct an ICE table for the reactiondetermine the direction the reaction is proceeding

  • For the reaction I2(g) + Cl2(g) 2 ICl(g) @ 25C, Kp = 81.9. If the initial partial pressures are all 0.100 atm, find the equilibrium concentrations +2xxx0.100x0.100x0.100+2x

    [I2][Cl2][ICl]initial0.1000.1000.100changeequilibrium

    represent the change in the partial pressures in terms of xsum the columns to find the equilibrium concentrations in terms of xsubstitute into the equilibrium constant expression and solve for x

  • For the reaction I2(g) + Cl2(g) 2 ICl(g) @ 25C, Kp = 81.9. If the initial partial pressures are all 0.100 atm, find the equilibrium concentrations +2xxx0.100x0.100x0.100+2x

    [I2][Cl2][ICl]initial0.1000.1000.100changeequilibrium

    substitute into the equilibrium constant expression and solve for x

  • For the reaction I2(g) + Cl2(g) 2 ICl(g) @ 25C, Kp = 81.9. If the initial partial pressures are all 0.100 atm, find the equilibrium concentrations +2xxx0.100x0.100x0.100+2x0.0270.0270.246-0.0729-0.07292(-0.0729)

    [I2][Cl2][ICl]initial0.1000.1000.100changeequilibrium

    substitute x into the equilibrium concentration definition and solve

  • -0.0729For the reaction I2(g) + Cl2(g) 2 ICl(g) @ 25C, Kp = 81.9. If the initial partial pressures are all 0.100 atm, find the equilibrium concentrations 0.0270.0270.246-0.07292(0.0729)Kp(calculated) = Kp(given) within significant figures

    [I2][Cl2][ICl]initial0.1000.1000.100changeequilibrium

    check by substituting the equilibrium concentrations back into the equilibrium constant expression and comparing the calculated K to the given K

  • For the reaction I2(g) 2 I(g) the value of Kc = 3.76 x 10-5 at 1000 K. If 1.00 moles of I2 is placed into a 2.00 L flask and heated, what will be the equilibrium concentrations of [I2] and [I]?(Hint: you will need to use the quadratic formula to solve for x)

  • For the reaction I2(g) 2 I(g) the value of Kc = 3.76 x 10-5 at 1000 K. If 1.00 moles of I2 is placed into a 2.00 L flask and heated, what will be the equilibrium concentrations of [I2] and [I]?since [I]initial = 0, Q = 0 and the reaction must proceed forward

    [I2][I]initial0.5000change-x+2xequilibrium0.500- x2x

  • For the reaction I2(g) 2 I(g) the value of Kc = 3.76 x 10-5 at 1000 K. If 1.00 moles of I2 is placed into a 2.00 L flask and heated, what will be the equilibrium concentrations of [I2] and [I]?

    [I2][I]initial0.5000change-x+2xequilibrium0.500- x2x

  • For the reaction I2(g) 2 I(g) the value of Kc = 3.76 x 10-5 at 1000 K. If 1.00 moles of I2 is placed into a 2.00 L flask and heated, what will be the equilibrium concentrations of [I2] and [I]?x = 0.002160.500 0.00216 = 0.498[I2] = 0.498 M2(0.00216) = 0.00432[I] = 0.00432 M

    [I2][I]initial0.5000change-x+2xequilibrium0.4980.00432

  • Approximations to Simplify the Mathwhen the equilibrium constant is very small, the position of equilibrium favors the reactantsfor relatively large initial concentrations of reactants, the reactant concentration will not change significantly when it reaches equilibriumthe [X]equilibrium = ([X]initial ax) [X]initial we are approximating the equilibrium concentration of reactant to be the same as the initial concentrationassuming the reaction is proceeding forward

  • Checking the Approximation and Refining as Necessarywe can check our approximation afterwards by comparing the approximate value of x to the initial concentrationif the approximate value of x is less than 5% of the initial concentration, the approximation is valid

  • For the reaction 2 H2S(g) 2 H2(g) + S2(g) @ 800C, Kc = 1.67 x 10-7. If a 0.500 L flask initially containing 1.25 x 10-4 mol H2S is heated to 800C, find the equilibrium concentrations.since no products initially, Qc = 0, and the reaction is proceeding forward

    [H2S][H2][S2]initial2.50E-400changeequilibrium

    Construct an ICE table for the reactiondetermine the direction the reaction is proceeding

  • For the reaction 2 H2S(g) 2 H2(g) + S2(g) @ 800C, Kc = 1.67 x 10-7. If a 0.500 L flask initially containing 1.25 x 10-4 mol H2S is heated to 800C, find the equilibrium concentrations.+x+2x2x2.50E-42x2xx

    [H2S][H2][S2]initial2.50E-400changeequilibrium

    represent the change in the partial pressures in terms of xsum the columns to find the equilibrium concentrations in terms of xsubstitute into the equilibrium constant expression

  • For the reaction 2 H2S(g) 2 H2(g) + S2(g) @ 800C, Kc = 1.67 x 10-7. If a 0.500 L flask initially containing 1.25 x 10-4 mol H2S is heated to 800C, find the equilibrium concentrations.+x+2x2x2.50E-42x2xx2.50E-4

    [H2S][H2][S2]initial2.50E-400changeequilibrium

    since Kc is very small, approximate the [H2S]eq = [H2S]init and solve for x

  • For the reaction 2 H2S(g) 2 H2(g) + S2(g) @ 800C, Kc = 1.67 x 10-7. If a 0.500 L flask initially containing 1.25 x 10-4 mol H2S is heated to 800C, find the equilibrium concentrations.+x+2x2x2xx2.50E-4the approximation is not valid!!

    [H2S][H2][S2]initial2.50E-400changeequilibrium

    check if the approximation is valid by seeing if x < 5% of [H2S]init

  • For the reaction 2 H2S(g) 2 H2(g) + S2(g) @ 800C, Kc = 1.67 x 10-7. If a 0.500 L flask initially containing 1.25 x 10-4 mol H2S is heated to 800C, find the equilibrium concentrations.+x+2x2x2.50E-42x2xxxcurrent = 1.38 x 10-5

    [H2S][H2][S2]initial2.50E-400changeequilibrium

    if approximation is invalid, substitute xcurrent into Kc where it is subtracted and re-solve for xnew

  • For the reaction 2 H2S(g) 2 H2(g) + S2(g) @ 800C, Kc = 1.67 x 10-7. If a 0.500 L flask initially containing 1.25 x 10-4 mol H2S is heated to 800C, find the equilibrium concentrations.+x+2x2x2.50E-42x2xxxcurrent = 1.27 x 10-5since xcurrent = xnew, approx. OK

    [H2S][H2][S2]initial2.50E-400changeequilibrium

    Substitute xcurrent into Kc where it is subtracted and re-solve for xnew. If xnew is the same number, you have arrived at the best approximation.

  • For the reaction 2 H2S(g) 2 H2(g) + S2(g) @ 800C, Kc = 1.67 x 10-7. If a 0.500 L flask initially containing 1.25 x 10-4 mol H2S is heated to 800C, find the equilibrium concentrations.+x+2x2x2.50E-42x2xxxcurrent = 1.28 x 10-52.24E-42.56E-51.28E-5

    [H2S][H2][S2]initial2.50E-400changeequilibrium

    substitute xcurrent into the equilibrium concentration definitions and solve

  • For the reaction 2 H2S(g) 2 H2(g) + S2(g) @ 800C, Kc = 1.67 x 10-7. If a 0.500 L flask initially containing 1.25 x 10-4 mol H2S is heated to 800C, find the equilibrium concentrations.+x+2x2x2.24E-42.56E-51.28E-5Kc(calculated) = Kc(given) within significant figures

    [H2S][H2][S2]initial2.50E-400changeequilibrium

    check by substituting the equilibrium concentrations back into the equilibrium constant expression and comparing the calculated K to the given K

  • For the reaction I2(g) 2 I(g) the value of Kc = 3.76 x 10-5 at 1000 K. If 1.00 moles of I2 is placed into a 2.00 L flask and heated, what will be the equilibrium concentrations of [I2] and [I]?(use the simplifying assumption to solve for x)

  • For the reaction I2(g) 2 I(g) the value of Kc = 3.76 x 10-5 at 1000 K. If 1.00 moles of I2 is placed into a 2.00 L flask and heated, what will be the equilibrium concentrations of [I2] and [I]?since [I]initial = 0, Q = 0 and the reaction must proceed forward

    [I2][I]initial0.5000change-x+2xequilibrium0.500- x2x

  • For the reaction I2(g) 2 I(g) the value of Kc = 3.76 x 10-5 at 1000 K. If 1.00 moles of I2 is placed into a 2.00 L flask and heated, what will be the equilibrium concentrations of [I2] and [I]?the approximation is valid!!

    [I2][I]initial0.5000change-x+2xequilibrium0.500- x2x

  • For the reaction I2(g) 2 I(g) the value of Kc = 3.76 x 10-5 at 1000 K. If 1.00 moles of I2 is placed into a 2.00 L flask and heated, what will be the equilibrium concentrations of [I2] and [I]?x = 0.002170.500 0.00217 = 0.498[I2] = 0.498 M2(0.00217) = 0.00434[I] = 0.00434 M

    [I2][I]initial0.5000change-x+2xequilibrium0.500- x2x

  • Disturbing and Re-establishingEquilibrium once a reaction is at equilibrium, the concentrations of all the reactants and products remain the samehowever if the conditions are changed, the concentrations of all the chemicals will change until equilibrium is re-establishedthe new concentrations will be different, but the equilibrium constant will be the sameunless you change the temperature

  • Le Chteliers PrincipleLe Chtelier's Principle guides us in predicting the effect various changes in conditions have on the position of equilibrium it says that if a system at equilibrium is disturbed, the position of equilibrium will shift to minimize the disturbance disturbances all involve making the system open

  • An Analogy: Population Changes

  • The Effect of Concentration Changes on EquilibriumAdding a reactant will decrease the amounts of the other reactants and increase the amount of the products until a new position of equilibrium is found that has the same KRemoving a product will increase the amounts of the other products and decrease the amounts of the reactants.you can use this to drive a reaction to completion! Equilibrium shifts away from side with added chemicals or toward side with removed chemicalsRemember, adding more of a solid or liquid does not change its concentration and therefore has no effect on the equilibrium

  • Disturbing Equilibrium:Adding or Removing Reactantsafter equilibrium is established, how will adding a reactant affect the rate of the forward reaction? How will it affect the rate of the reverse reaction? What will this cause? How will it affect the value of K?as long as the added reactant is included in the equilibrium constant expressioni.e., not a solid or liquidafter equilibrium is established, how will removing a reactant affect the rate of the forward reaction? How will it affect the rate of the reverse reaction? What will this cause? How will it affect the value of K?

  • Disturbing Equilibrium:Adding Reactantsadding a reactant initially increases the rate of the forward reaction, but has no initial effect on the rate of the reverse reaction. the reaction proceeds to the right until equilibrium is re-established. at the new equilibrium position, you will have more of the products than before, less of the non-added reactants than before, and less of the added reactant but not as little of the added reactant as you had before the additionat the new equilibrium position, the concentrations of reactants and products will be such that the value of the equilibrium constant is the same

  • Disturbing Equilibrium:Removing Reactantsremoving a reactant initially decreases the rate of the forward reaction, but has no initial effect on the rate of the reverse reaction. so the reaction is going faster in reversethe reaction proceeds to the left until equilibrium is re-established. at the new equilibrium position, you will have less of the products than before, more of the non-removed reactants than before, and more of the removed reactant but not as much of the removed reactant as you had before the removalat the new equilibrium position, the concentrations of reactants and products will be such that the value of the equilibrium constant is the same

  • The Effect of Adding a Gas to a Gas Phase Reaction at Equilibriumadding a gaseous reactant increases its partial pressure, causing the equilibrium to the rightincreasing its partial pressure increases its concentrationdoes not increase the partial pressure of the other gases in the mixtureadding an inert gas to the mixture has no effect on the position of equilibriumdoes not effect the partial pressures of the gases in the reaction

  • The Effect of Concentration Changes on EquilibriumWhen NO2 is added, some of it combines to make more N2O4

  • The Effect of Concentration Changes on EquilibriumWhen N2O4 is added, some of itdecomposes to make more NO2

  • Effect of Volume Changeon Equilibriumdecreasing the size of the container increases the concentration of all the gases in the containerincreases their partial pressuresif their partial pressures increase, then the total pressure in the container will increaseaccording to Le Chteliers Principle, the equilibrium should shift to remove that pressurethe way the system reduces the pressure is to reduce the number of gas molecules in the containerwhen the volume decreases, the equilibrium shifts to the side with fewer gas molecules

  • Disturbing Equilibrium:Changing the Volumeafter equilibrium is established, how will decreasing the container volume affect the total pressure of solids, liquid, and gases? How will it affect the concentration of solids, liquid, solutions, and gases? What will this cause? How will it affect the value of K?

  • Disturbing Equilibrium: Reducing the Volumefor solids, liquids, or solutions, changing the size of the container has no effect on the concentration, therefore no effect on the position of equilibriumdecreasing the container volume will increase the total pressureBoyles Lawif the total pressure increases, the partial pressures of all the gases will increaseDaltons Law of Partial Pressuresdecreasing the container volume increases the concentration of all gasessame number of moles, but different number of liters, resulting in a different molaritysince the total pressure increases, the position of equilibrium will shift to decrease the pressure by removing gas moleculesshift toward the side with fewer gas moleculesat the new equilibrium position, the partial pressures of gaseous reactants and products will be such that the value of the equilibrium constant is the same

  • The Effect of Volume Changes on Equilibrium

  • The Effect of Temperature Changes on Equilibrium Positionexothermic reactions release energy and endothermic reactions absorb energyif we write Heat as a product in an exothermic reaction or as a reactant in an endothermic reaction, it will help us use Le Chteliers Principle to predict the effect of temperature changeseven though heat is not matter and not written in a proper equation

  • The Effect of Temperature Changes on Equilibrium for Exothermic Reactionsfor an exothermic reaction, heat is a productincreasing the temperature is like adding heataccording to Le Chteliers Principle, the equilibrium will shift away from the added heatadding heat to an exothermic reaction will decrease the concentrations of products and increase the concentrations of reactantsadding heat to an exothermic reaction will decrease the value of Khow will decreasing the temperature affect the system?aA + bB cC + dD + Heat

  • The Effect of Temperature Changes on Equilibrium for Endothermic Reactionsfor an endothermic reaction, heat is a reactantincreasing the temperature is like adding heataccording to Le Chteliers Principle, the equilibrium will shift away from the added heatadding heat to an endothermic reaction will decrease the concentrations of reactants and increase the concentrations of productsadding heat to an endothermic reaction will increase the value of Khow will decreasing the temperature affect the system?Heat + aA + bB cC + dD

  • The Effect of Temperature Changes on Equilibrium

  • Not Changing the Position of Equilibrium - Catalysts catalysts provide an alternative, more efficient mechanismworks for both forward and reverse reactionsaffects the rate of the forward and reverse reactions by the same factortherefore catalysts do not affect the position of equilibrium

  • Practice - Le Chteliers PrincipleThe reaction 2 SO2(g) + O2(g) 2 SO3(g) with DH = -198 kJ is at equilibrium. How will each of the following changes affect the equilibrium concentrations of each gas once equilibrium is re-established?adding more O2 to the containercondensing and removing SO3compressing the gasescooling the containerdoubling the volume of the containerwarming the mixtureadding the inert gas helium to the containeradding a catalyst to the mixture

  • Practice - Le Chteliers PrincipleThe reaction 2 SO2(g) + O2(g) 2 SO3(g) with DH = -198 kJ is at equilibrium. How will each of the following changes affect the equilibrium concentrations of each gas once equilibrium is re-established?adding more O2 to the containershift to SO3condensing and removing SO3shift to SO3compressing the gasesshift to SO3cooling the containershift to SO3doubling the volume of the containershift to SO2warming the mixtureshift to SO2adding helium to the containerno effectadding a catalyst to the mixtureno effect

  • Contoh soal :0,1 mol HI dimasukkan dalam tabung 1 lt dan terurai sesuai reaksi : 2HI H2 + I2. Jika I2 yang terbentuk adalah 0,02 mol, berapa harga K?

    2. Tetapan kesetimbangan untuk reaksi : A + 2B AB2 adalah 0,25. Berapa jumlah mol A yang harus dicampurkan pada 4 mol B dalam volume 5 lt agar menghasilkan 1 mol AB2.

  • Jawaban no 1.

  • Jawaban no.2Misal mol A mula-mula = x mol A + 2B AB2Mula-mula: x 4Terurai : 1 2Setimbang: x-1 4-2 = 2 1

    [AB2] = mol / lt = 1 / 5 lt = 1/5[A] = mol / lt = x-1 / 5 lt = (x-1)/5[2B] = mol / lt = 2 / 5 lt = 2/5K = [AB2] = 1/5 x = 26 [A] [B]2 (x-1)/5 (2/5)2

  • Soal-soal :Tetapan kesetimbangan untuk reaksi : 2HBr H2 + Br2 adalah . Hitunglah mol H2 yang dihasilkan jika 2 mol HBr dimasukkan dalam tabung 2 liter.

    1 mol A dan 1 mol B direaksikan dalam tabung 1 liter, sesuai dengan reaksi A + B C + D ternyata pada saat setimbang diperoleh 0,33 mol A. Berapa harga K?

  • Soal-soal :Tetapan kesetimbangan CO + H2O CO2 + H2 adalah 0,1. Berapa jumlah mol CO yang harus dicampurkan pada 3 mol H2O dalam volume 1 liter agar menghasilkan 2 mol H2.

    *****************************************if in addition you calculate Kp from Kc you find that it is 2.26, slightly greater than 1 showing that the equilibrium constant may be unreliable for predicting the position of equilibrium when it is close to 1*********************************************