Lecture 34: Temperature Dependence of Rate Constant | Lecture Note - Edubirdie

University:
Massachusetts Institute of Technology
Course:
5.60 | Thermodynamics & Kinetics
Academic year:

2024
Views:

402

Pages:

4
Author:

Toby Blackburn

5.60 Spring 2007 Lecture #34 page 1 Temperature Dependence of Rate Constant Arrhenius Law k = Ae −Ea / RT where Ea ≡ Activation Energy A ≡ Pre-Exponential Factor lnk(T) k(T) k=A Slope=-Ea/R T Typically: Ea ~ 50-300 kJ/mole A (unimolecular) ~ 1012–1015 sec-1 (bimoledular) ~ 1011 liter/(mole sec) T 5.60 Spring 2007 Lecture #34 page 2 Physical Interpretation of Ea Consider A→ ←B A+B→C Reactants B)* (A ⇒ Activated Complex (A C ⇒ Product B)* Eaforward Eabackward Energy Reactants Products Reaction Coordinate Small Ea ⇒ Weak T dependence ⇒ Fast reaction Large Ea ⇒ Strong T dependence ⇒ Slow reaction 5.60 Spring 2007 Lecture #34 page 3 Catalysis A catalyst speeds up a reaction but is NOT destroyed or used up in the process Consider A k1 k-1 (k1,k-1) both slow B Let C be a catalyst A+C k2 k-2 B+C (k2,k-2) both fast C acts to LOWER the Ea for the reaction, often altering the mechanism. A ⇒ A* B ⇒ Uncatalyzed A+C ⇒ (A Catalyzed C)* ⇒ B+C 5.60 Spring 2007 Lecture #34 page 4 A* Ea C)* (A Energy E aC A B Reaction Coordinate The Equilibrium Keq = [B]eq/[A]eq is unaltered Only the rate is changed through a lowering of Ea.

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