Week 2: Chemical Kinetics 2 Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Experiments Index ChemLab Home		Prelab Problems 1. Assume that run (i) was carried out and the following data were obtained: t/min A565 5 0.25 10 0.18 15 0.11 20 0.06 Plot the data and extrapolate to find the value of t. Calculate the rate of the reaction in units of M s-1, from the change in concentration and the exptrapolated value of t. This rate equals k'. From k' and the concentrations of cyclohexanone and H+, calculate a value for the reaction rate constant k. Be sure to calculate the intial and final concentrations of cyclohexanone and H+ and use their average values to calculate k, as in the example, above. The concentration information you need is in the table of conditions, for run (i). 2. Suppose that reaction mixture (ii), from last week, had been carried out at T(1) = 25 °C and T(2) = 5 °C with t(1) = 950 s and t(2) = 3800 s as the times required for disappearance of the triiodide color. How could you increase the rate of reaction at the lower temperature to a more reasonable value? What change in [H+] would be required to reduce the time of reaction by 1/2? What would you expect to be the final time if all the water in the reaction mixture were replaced with HCl? 3.The following values were obtained for the rate constant at 25 °C. for runs i-v: 3.15 × 10-4 M-1 s-1 3.44 × 10-4 M-1 s-1 3.29 × 10-4 M-1 s-1 3.11 × 10-4 M-1 s-1 3.01 × 10-4 M-1 s-1 Calculate the mean value of k at this temperature, the standard deviation, and the 95% confidence interval. After determining the rate constant at a series of different temperatures, an Arrhenius plot was made and it was found to have a slope of -11,000 ± 2000 (95%, n=4). What are the units of the slope? Calculate the value of Ea for the data and calculate the uncertainty in Ea using error propagation.
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