lecnotes34 - MIT OpenCourseWare http:/ocw.mit.edu 5.111...

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MIT OpenCourseWare http://ocw.mit.edu 5.111 Principles of Chemical Science Fall 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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34.1 5.111 Lecture 34 Kinetics Topics: Effect of Temperature, Collision Theory, Activated Complex Theory. Chapter 13.11-13.13 Effect of Temperature on Reaction Rates Gas-Phase A qualitative observation is that reaction rates tend to increase with increased temperature. Now we will consider the quantitative effect. In 1889, Svante Arrhenius plotted rate constants (k) versus temperature. He found that plotting ln k versus inverse temperature gave a straight line. k = rate constant intercept = ln A T = temperature A = factor A or pre-exponential factor (same units as k) E a = activation energy slope = -E a R = gas constant ln k R ln k = -E + ln A a RT y = mx + b 1 K -1 T Rate constants vary ____________________ with inverse temperature A and E a depend on the reaction being studied. Is factor A temperature dependent? Is E a temperature dependent?
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E min High temperature Low temperature Kinetic energy Fraction of molecules 34.2 ln k = ln A - E a RT Arrhenius equation ln k = -E a + ln A can also be written RT or k = Ae -E a /RT What is E a , activation energy? Consider CH 3 (g) + CH 3 (g) C 2 H 6 (g) 2 molecules collide to form product (bimolecular) but every two molecules that collide won't form product. Why? Only those collisions for which the collision energy exceeds some critical energy (_________________ energy) result in a reaction.
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lecnotes34 - MIT OpenCourseWare http:/ocw.mit.edu 5.111...

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