Experiment 2: Factors Affecting Rates
Experiment 2: Factors Affecting Reaction RatesObjective: Part A ‐ To determine the effect of concentration on therate of formation of Iodine, I2, and therefore,determine the reaction’s rate law.Part B ‐ To study the effect of temperature on the rate ofa reaction.Part C ‐ To study the effect of a catalyst on the rate ofa reaction.
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesObjective: Part A ‐ To determine the effect of concentration on therate of formation of Iodine, I2 , and therefore, determine thereaction’s rate law.Iodine clock ReactionS2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)(clear solution)(pale yellow solution)Reactants:Ammonium persulfate(NH4)2S2O8Potassium iodideKICHEM 0012 Lecture Notes2
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesObjective: Part A ‐ To determine the effect of concentration on therate of formation of Iodine, I2 , and therefore, determine thereaction’s rate law.How do we do this?Iodine clock ReactionS2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)(clear solution)(pale yellow solution)Observe a COLOUR CHANGE!Problem: The pale yellow solution is visually very difficult to judge.CHEM 0012 Lecture Notes3
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesObjective: Part A ‐ To determine the effect of concentration on therate of formation of Iodine, I2 , and therefore, determine thereaction’s rate law.How do we do this?Iodine clock ReactionS2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)(clear solution)(pale yellow solution)Introduce two substances to help us observe the colour changemore accurately:1. Starch indicator2. Sodium thiosulfate, Na2S2O3, of a fixed quantityCHEM 0012 Lecture Notes4
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesObjective: Part A ‐ To determine the effect of concentration on therate of formation of Iodine, I2 , and therefore, We time how long itdetermine the reaction’s rate law.takes for thesolution to turncolour.Iodine clock ReactionS2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)(clear solutionI2 (aq) 2 S2O32‐(aq)thiosulfate ionI2 (aq) starch(1))S4O62‐ (aq) 2 I‐ (aq)iodine‐starch complex(2)(3)(coloured solution )As the I2 is formed (1), it reacts with the fixed amount of sodium thiosulfate that hasbeen added to the reaction mixture (2). When the sodium thiosulfate is used up,the next quantity of I2 that is formed reacts with the starch indicator to form a colourcomplex, and turns the clear solution into a coloured solution (3).CHEM 0012 Lecture Notes5
Reaction KineticsHebden – Unit 1 (page 1‐34)Make solutions ofdifferentconcentrations.Experiment 2: Factors Affecting Reaction RatesObjective: Part A ‐ To determine the effect of concentration on the rateof formation of Iodine, I2, and therefore, determine thereaction’s rate law.Iodine clock ReactionS2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)Prepare 14 solutions in 14 Erlenmeyer flasks withdifferent concentrations of S2O82‐ and I‐ solutions!Label them:A1, A2, A3, A4, A5, A6, A7.B1, B2, B3, B4, B5, B6, B7.SEPARATE the reactants until we are ready to mix them!KI (I‐) in ‘A’ solutions;(NH4)2S2O8 (S2O82‐) in ‘B’ solutionsCHEM 0012 Lecture Notes6
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesIodine clock ReactionTotal volume of ‘A’solutions 30.0 mL.S2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)CHEM 0012 Lecture Notes7
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesIodine clock ReactionTotal volume of ‘B’solutions 20.0 mL.S2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)CHEM 0012 Lecture Notes8
Reaction KineticsTotal volume of thecombined solution Hebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesIodine clock Reaction50.0 mL.S2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)MIX and TIME:A1 B1A2 B2(expt 1)(expt 2)A3 B3(expt 3)A4 B4A5 B5A6 B6A7 B7(expt 4)(expt 5)(expt 6)(expt 7)CHEM 0012 Lecture Notes9
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesWhen solutions A1 and B1 are combined, what is the concentration of(NH4)2S2O8 in moles/L?(0.0050 L) x (0.100 moles/L) 0.00050 moles (NH4)2S2O80.00050 moles (NH4)2S2O8 0.010 M (NH4)2S2O80.0500 Lin the combinedA1 B1 solutionTotal volume of thecombined solution 50.0 mL.CHEM 0012 Lecture Notes10
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesFollow the example on the previous slide and calculate the concentrationsof (NH4)2S2O8 in moles/L when A2 B2, A3 B3, A4 B4, A5 B5, A6 B6 andA7 B7 are combined?(0.0050 L) x (0.100 moles/L) 0.00050 moles(NH4)2S2O80.00050 moles (NH4)2S2O8 0.010 M (NH4)2S2O80.0500 LNote: The concentrations of (NH4)2S2O8 should bethe same for the A4/B4, A5/B5, A6/B6 and A7/B7solutions because the B4, B5, B6, and B7 solutionseach contains 20.0 mL of (NH4)2S2O8 .CHEM 0012 Lecture Notes11
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesFollow the example on the previous slide and calculate the concentrationsof (NH4)2S2O8 in moles/L when A2 B2, A3 B3, A4 B4, A5 B5, A6 B6 andA7 B7 are combined?Enter concentrations in Table 2-4 and Table 2-6 in the post-lab questions ofExperiment 2.Note: The concentrations of (NH4)2S2O8 should be the samefor the A4/B4, A5/B5, A6/B6 and A7/B7 solutions.CHEM 0012 Lecture Notes12
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesWhen solutions A1 and B1 are combined, what is the concentration ofKI in moles/L?(0.0200 L) x (0.200 moles/L) 0.00400 moles KI0.00400 moles KI 0.0800 M KIin the combined0.0500LA1 B1 solutionTotal volume of thecombined solution 50.0 mL.CHEM 0012 Lecture Notes13
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesFollow the example on the previous slide and calculate theconcentrations of KI in moles/L when A2 B2, A3 B3, A4 B4, A5 B5,A6 B6 and A7 B7 are combined?(0.0200 L) x (0.200 moles/L) 0.00400 moles KI0.00400 moles KI 0.0800 M KI0.0500LNote: The concentrations of KI should bethe same for the A1/B1, A2/B2, A3/B3 andA4/B4 solutions because the A1, A2, A3, and A4solutions each contains 20.0 mL of KI.CHEM 0012 Lecture Notes14
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesFollow the example on the previous slide and calculate theconcentrations of KI in moles/L when A2 B2, A3 B3, A4 B4, A5 B5,A6 B6 and A7 B7 are combined?Enter concentrations in Table 2-4 and Table 2-6 in the post-lab questions ofExperiment 2.Note: The concentrations of KI should be the same for the A1/B1,A2/B2, A3/B3 and A4/B4 solutions .CHEM 0012 Lecture Notes15
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesHow many moles of Na2S2O3 are available?(0.0100 L) x (0.00500 moles/L) 0.0000500 moles Na2S2O3This is the same amount of Na2S2O3that is added to ALL the ‘A’ solutions.CHEM 0012 Lecture Notes16
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesIodine clock ReactionS2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)(clear solution1 I2 (aq) 2 S2O32‐(aq)thiosulfate ion(1))S4O62‐ (aq) 2 I‐ (aq)(clear solution(2))How many moles of I2 will consume the Na2S2O3 added?From the previous slide, we calculated that there is 0.0000500 molesNa2S2O3 in each ‘A’ solution.From equation (2), the I2 and S2O32‐ is 1:2.It takes 0.0000500/2 0.0000250 moles of I2 to consume the S2O32‐.CHEM 0012 Lecture Notes17
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesWhat is the concentration of I2 when the Na2S2O3 is consumed?From the previous slide, we calculated that it takes0.0000250 moles of I2 to consume the S2O32‐.0.0000250 moles I2 0.000500 M I20.0500LTotal volume of thecombined solution 50.0 mL.When you time how long it takes for thesolution to turn colour, you are actuallytiming how long it takes to produce0.000500 M I2 !!!Remember this number. You’ll need the [I2] in the rate calculation.CHEM 0012 Lecture Notes18
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesObjective: Part A ‐ To determine the effect of concentration on therate of formation of Iodine, I2 , and therefore, determine thereaction’s rate law.Iodine clock ReactionS2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)(clear solution)(pale yellow solution)What is a reaction’s rate law?CHEM 0012 Lecture Notes19
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesWhat is a reaction’s rate law?Iodine clock ReactionS2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)The rate law for a chemical reaction is an experimentally determinedmathematical equation that describes the progress of the reaction.For the Iodine clock reaction, the reaction rate of formation of I2 is proportionalto the product of the concentrations each reactant each raised to some power, x and y.Rate [S2O82‐]x [I- ]yCHEM 0012 Lecture Notes20
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesWhat is a reaction’s rate law?Iodine clock ReactionS2O82‐ (aq) 2 I‐ (aq) 2 SO42‐ (aq) I2 (aq)Rate [S2O82‐]x [I- ]yWe can remove the proportional symbol and introduce a proportionality constant, k.Rate k [S2O82‐]x [I- ]yThe proportionality constant, k, is known as the rate constant.We will experimentally determine the values of x and y.CHEM 0012 Lecture Notes21
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesObjective: Part A ‐ To determine the effect of concentration on therate of formation of Iodine, I2 , and therefore, determine thereaction’s rate law.Table 2-4 Sample oles/L)[I‐](moles/L)1A1/B1264*0.01000.0800Rate offormation of I2(moles/L)* Sample data[I 2 ] formed 0.000500 M 1.89 x 10 -6 M/sRate of formation of I 2 264 stimeCHEM 0012 Lecture Notes22
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesTable 2-4 Sample oles/L)1A1/B12640.01002A2/B2122*0.0200* Sample data[I‐](moles/L)Rate offormation ofI2 (moles/L)1.89 x 10‐60.08004.09 x 10‐6Similarly, we can calculate theRate of formation of I2 for expt 2.CHEM 0012 Lecture Notes23
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesTable 2-5 Sample Calculation of ‘x’Experimentpairs‘x’, the order of the reactionwith respect to [S2O82‐]Average value of‘x’1 and 2Rate k [S2O82‐]x [I- ]yExpt 1:1.89 x 10 -6Expt 2:-64.09 x 10 1 0.464 2 k [S 2 O 8 2 ] x [I - ] y2 x- y k [S 2 O 8 ] [I ]x0.464 0.5xCHEM 0012 Lecture Notesk (0.0100) x (0.0800) yk (0.0200) x (0.0800) yX 1.1124
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesSimilar calculation can be carried out to calculate ‘y’ for Table 2-7.Rate k [S2O82‐]x [I- ]y‘x’ is the “order of the reaction with respect to S2O82-”‘y’ is the “order of the reaction with respect to I-”‘x y’ is the “overall order of the reaction”CHEM 0012 Lecture Notes25
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesOnce ‘x’ and ‘y’ are determined, we can calculate the rate constant, k.Table 2-9 Sample CalculationExperimentRate constant, kAverage value of k11.89 x 10‐6 k (0.0100)x (0.0800)ySubstitute ‘x’ and ‘y’ and solve for k.CHEM 0012 Lecture Notes26
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesObjective: Part B ‐ To study the effect of temperature on the rateof a reaction.How do we do this?Keep the concentrations of the reactants constant, but let theReaction react at different temperatures:0oC, 20oC, 30oC, 40oCUse A4, B4 solutions for all the temperatures!!Part B calculations for Table 2-10 is similar to Part A.CHEM 0012 Lecture Notes27
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesObjective: Part B ‐ To study the effect of temperature on the rateof a reaction.Verify Arrhenius’ Equationk AeEact RTA is the pre-exponential or frequency factor, a constant related to the collision frequencyR is the gas constant (8.314 J / K mole)T is the absolute temperature (K)k is the rate constant at temperature TEact is the activation energy, the energy required by the reacting species for theircollisions to be effective (ie - those that lead to the formation of products)CHEM 0012 Lecture Notes28
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesObjective: Part B ‐ To study the effect of temperature on the rateof a reaction.Rewrite Arrhenius’ Equationk Ae EactRTE actln k Ry1Plot " ln k versus "T m 1 ln A T x bshould yield a straight line!!CHEM 0012 Lecture Notes29
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesObjective: Part B ‐ To study the effect of temperature on the rateof a reaction.Ea Ea RmRb ln( A) A ebm CHEM 0012 Lecture Notes30
Reaction KineticsHebden – Unit 1 (page 1‐34)Experiment 2: Factors Affecting Reaction RatesObjective: Part C ‐ To study the effect of a catalyst on the rate ofa reaction.Use the A4, B4 solutions and add copper as a catalyst.A catalyst speeds up a reaction.When Cu is added, by how many times does the reaction increase?Rate of formation of I 2 with Cu added 1Rate of formation of I 2 without CuData from Part B.CHEM 0012 Lecture Notes31
colour. ( coloured solution ) Objective: Part A ‐To determine the effect of concentration on the rate of formation of Iodine, I 2 , and therefore, determine the reaction’s rate law. I 2 (aq)
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