lecnotes35 - 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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__________________________________________________________________________________ __________________________________________________________________________________ 35.1 5.111 Lecture 35 Kinetics Topic: Catalysis Chapter 13 (Section 13.14-13.15) From Friday’s material Le Chatelier's Principle - when a stress is applied to a system in equilibrium, the equilibrium tends to adjust to minimize the effect of the stress. Increasing the temperature can cause reaction to shift in endothermic direction. P.E. P.E. reaction coordinate reaction coordinate E a,f E a,r product reactants endothermic products reactants E a, f E a, r exothermic ! E = E a,f - E a,r ! E = E a,f - E a,r + (endo) = big number - small number - (exo) = small number - large number increase temperature, easier to overcome increase temperature, easier to overcome E a,f . Equilibrium shifts toward products E a,r . Equilibrium shifts toward reactants in for endothermic reaction. the exothermic reaction. most molecules have enough energy to overcome small barriers increasing temperature allows more molecules to overcome larger barriers Recall, a large E a means that the rate constant is very sensitive to changes in temperature. Big E a - increasing the temperature makes a _______ difference Small E a - increasing the temperature does not make much of a difference. End of Friday’s material
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35.2 Kinetics of Catalysis A catalyst is a substance that takes part in a chemical reaction and speeds it up, but doesn't undergo any permanent change itself.
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lecnotes35 - MIT OpenCourseWare http/ocw.mit.edu 5.111...

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