Assigned problems _4

# Assigned problems _4 - a and A from three pairs of rate...

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Chemistry 2080 Spring 2010 Problem Set #4 - due date: Friday February 26th at 2 pm Name:________________ Lab TA Name:__________________ Lab Day/Time:______________________ 1) If you want to get an idea of the rate of a reaction that is extraordinarily slow at room temperature, one thing that you can do is to raise the temperature, measure several rates, and then extrapolate to room temperature. As an example of a slow reaction, at room temperature, hydroxide reacts so slowly with a simple phosphate diester (e.g. dimethyl phosphate) that the hydroxide reacts more rapidly with pyrex glass than it does with the phosphate ester. Listed below are some rate constants that were collected at elevated temperatures. Please calculate the energy of activation (E a ) and the pre-exponential factor (the frequency factor, A) from these data, and then calculate the likely rate constant for the same reaction at 25.00°C. (Either use all four data points in a linear fit - best done on a computer or graphing calculator - or calculate three independent values of E

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Unformatted text preview: a and A from three pairs of rate constants, and then average the results. Say which method you use). Temperature °C Rate constant (L/mol.sec) 195.0 2.041 x 10-7 215.0 8.891 x 10-7 235.0 3.462 x 10-6 255.0 1.214 x 10-5 2) The compound azomethane decomposes at 300°C to form nitrogen and ethane: CH 3-N=N-CH 3 (g) –––––––> N 2 (g) + C 2 H 6 (g) This reaction was followed by monitoring the total pressure (P tot in mm of mercury) of the vessel in which the reaction was occurring. At t=0 there is only azomethane present. The following data were obtained: time (seconds) P tot (mm Hg) 0.00 284 100.0 348 150.0 375 200.0 398 250.0 418 300.0 436 Determine the order of the reaction with respect to the azomethane, i.e. is it zero order, first order, or second order? Determine the rate constant for the reaction at 300°C, and then calculate what the total pressure in the vessel was at 50.00 seconds after the start of the reaction....
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Assigned problems _4 - a and A from three pairs of rate...

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