5_60_lecture34

5_60_lecture34 - Small E a Weak T dependence Fast reaction...

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MIT OpenCourseWare http://ocw.mit.edu 5.60 Thermodynamics & Kinetics Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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5.60 Spring 2008 Lecture #34 page 1 Temperature Dependence of Rate Constant Arrhenius Law k = Ae E a /RT where E a Activation Energy A Pre-Exponential Factor T k(T) T lnk(T) k=A Slope=-E a /R Typically: E a ~ 50-300 kJ/mole A ( u n i m o l e c u l
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5.60 Spring 2008 Lecture #34 page 2 Physical Interpretation of E a Consider A + B C A → ← B (A B) * C Reactants Activated Complex Product Energy Reactants Products E a forward E a backward (A B) * Reaction Coordinate
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Unformatted text preview: Small E a Weak T dependence Fast reaction Large E a Strong T dependence Slow reaction 5.60 Spring 2008 Lecture #34 page 3 Catalysis A catalyst speeds up a reaction but is NOT destroyed or used up in the process k 1 Consider A B (k 1 ,k-1 ) both slow k-1 Let C be a catalyst k 2 A + C B + C (k 2 ,k-2 ) both fast k-2 C acts to LOWER the E a for the reaction, often altering the mechanism. A A* B Uncatalyzed A + C (A C)* B + C Catalyzed 5.60 Spring 2008 Lecture #34 page 4 (A C) * Energy A B E a A * E a C Reaction Coordinate The Equilibrium K eq = [B] eq /[A] eq is unaltered Only the rate is changed through a lowering of E a ....
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5_60_lecture34 - Small E a Weak T dependence Fast reaction...

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