Lecture+n - Ch 14 Recap Kinetics The reaction rate rate =...

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Unformatted text preview: Ch 14 Recap Kinetics The reaction rate rate = [A] t = [B] t A B [x] t dx dt lim t The instantaneous rate time rate here, lower slope, slower rate rate here, higher slope, faster rate [ ] But rate will change as the concentrations of reactants and products change! Ch 14 Recap Kinetics For a general reaction, a normalized rate can be obtained: aA + bB cC + dD rate = [A] t 1 a [B] t 1 b = = [C] t 1 c = [D] t 1 d The rate law is the expression which ties all of the rate dependence together. rate = k [A] x [B] y Practice problem #41 For the reaction F 2 (g) + 2 ClO 2 (g) 2 FClO 2 (g), the rate law is experimentally determined to be: rate = k [F 2 ] [ClO 2 ]. From the exponents in the rate law: 1 st order in F 2 (exponent is 1) 1 st order in ClO 2 (exponent is 1) 2 nd order overall (sum of exponents is 2) What is the order with respect to F 2 , ClO 2 , and overall? Ch 14 Recap Kinetics Experimentally determining rate laws method of initial rates Make initial conditions isolate the dependence of one reactants Use the ratio between two of the trials can be used to determine the order of the reaction with respect to the isolated reactant! Practice problem #42 Using the general reaction A + B C and the data below, determine the order of the reaction with respect to A and B, and the value of the rate constant, k, for this reaction. Trial [A] [B] initial rate, M s 1 1 2 3 0.01 0.01 0.02 0.01 0.02 0.02 4 10 4 4 10 4 11.3 10 4 Idea: solve for dependences in changes of concentration between runs compare trials 1 and 2 for dependence of B compare trials 2 and 3 for dependence of A Ch 14 Recap Kinetics Practice problem #42 Using the general reaction A + B C and the data below, determine the order of the reaction with respect to A and B, and the value of the rate constant, k, for this reaction. Looking at the reaction, the rate law takes the general form: rate = k [A] x [B] y Trial [A] [B] initial rate, M s 1 1 2 3 0.01 0.01 0.02 0.01 0.02 0.02 4 10 4 4 10 4 11.3 10 4 Lets make a ratio of the first two rate expressions: rate 1 rate 2 = k [A] x [B] y k [A] x [B] y = k (0.01) x (0.01) y k (0.01) x (0.02) y = (0.01) y (0.02) y = (0.5) y From this: rate 1 rate 2 = (0.5) y 4 10 4 4 10 4 = (0.5) y 1 = (0.5) y y = 0 zero order in B Practice problem #42 Using the general reaction A + B C and the data below, determine the order of the reaction with respect to A and B, and the value of the rate constant, k, for this reaction. Trial [A] [B] initial rate, M s 1 1 2 3 0.01 0.01 0.02 0.01 0.02 0.02 4 10 4 4 10 4 11.3 10 4 Ok, now lets make a ratio of the last two rate expressions: rate 2 rate 3 = k [A] x [B] y k [A] x [B] y = k (0.01) x (0.02) y k (0.02) x (0.02) y = (0.01) x (0.02) x = (0.5) x From this: rate 2 rate 3 = (0.5) x 4 10 4 11.3 10 4 = (0.5) x...
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This note was uploaded on 11/04/2009 for the course CHEM Chem 1C taught by Professor Farmer during the Spring '09 term at UCL.

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Lecture+n - Ch 14 Recap Kinetics The reaction rate rate =...

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