PCHEM Workshop 10 Notes

Updated: Dec 30, 2019

Tenth workshop with Dineli for Physical Chemistry (CHEM 3321) with Dr. Nielsen at UT Dallas!

NOTE: Check out that last page of my notes. I think we might have a question similar to the last one on the upcoming exam. Dineli spent some extra time reviewing how to solve a similar *hypothetical* problem, saying “if you had something like this on your test…” while working through it… so be sure you understand how to get the answer AND how to draw the graph.

As always, feel free to reach out to me for anything and I’ll try to get back to you as quickly as possible! Not sure why, but I don’t always get notifications for GroupMe, so if you need to reach me urgently, feel free to comment below or send me a message on Instagram ~ I always get push notifications for those two!

WORKSHOP WITH DINELI | November 12, 2019

Be sure to check Dineli’s page for her notes online. These are not the complete answers for the problem set. Make sure you plug and chug to get the individual answers! Also, verify any answers shown here — Dineli always stresses that we should verify the calculations from workshop!

Problem 1 Consider A(aq) + B(aq) P(aq) (1) with forwards and backwards rate constants k1 and k−1 respectively. A temperature-jump experiment is performed where the relaxation time constant is measured to be 310 µs, resulting in an equilibrium where Keq = 0.70 with [P]eq = 0.2M. What are k1 and k−1? You may assume that [A] = [B]. Note: the equations governing the kinetics are slightly different than we did in class because there are two species on the reactant side; you can consult the textbook for this case.

Problem 2 Calculate the relaxation time when 0.015 M benzoic acid is subjected to a temperaturejump experiment to a final temperature of 298 K. For the reaction H+ + C6H5COO− –> C6H5COOH (2) the rate constants are k1 = 3.5 × 1010 dm3 mol−1 s −1 and k−1 = 2.2 × 106 s −1 . If needed, you can look up the acid dissocation constant Ka, using any source.

Problem 3 A certain reaction is first order. 540 seconds after initiation of the reaction, 32.5% of the reactant remains. (a) What is the rate constant for this reaction? (b) At what time after initiation of the reaction will 10% of the reactant remain?

Problem 4 A first order decomposition reaction is observed to have the following rate constants at the indicated temperatures. Estimate the activation energy. k/(10−3 s −1 ) 2.46 45.1 576 T/◦C 0.0 20.0 40.0

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