Chemical Kinetics

1. Chemical Kinetics

2. Chemical Reactions • A and B are reactants, whose concentration decreases until the completion of the reaction. • C is a product, whose concentration increases until the completion of the reaction. • The rate at which the concentration of reactants decreases and the concentration of the product increases is is reaction rate. A + BC

3. Effect of Concentration, Temperature, and Catalysts • The greater the concentration of reactants the likelihood that molecules will collide increases. • At high temperatures, reactant molecules have more kinetic energy and have a greater chance of colliding. • Catalysts speed up reactions by changing the mechanism by which they occur. A + BC

4. Chemical Reactions • How can we represent the concentrations of molecules in a solution? • How can we keep track of the changes in concentrations? A + B C

5. Reaction Rate • We represent the concentration change over time as differential equations. Rate = - 1Δ [A] = - 1Δ[B] = 1Δ [C] a Δt b Δt c Δt Reactants decrease Products increase (negative) (positive) aA + bBcC

6. Rate Laws • Rate laws show the relationship between the reaction rate and the concentrations of reactants. • k is a constant that has a specific value for each reaction. It’s value is determined experimentally. rate = k [reactants] rate = k [A]α [B]β A + BC

7. Rate Laws • rate = k [A] [B] • The overall order of a reaction is determined by the sum of the exponents. • In this case the reaction is second order. Write a rate for the above reaction and state its overall order. A + BC A + B + CD

8. Integrating Rate Laws AB • First order rate laws can be written as : rate = - d [A] = k [A] d t • Integration of this rate law produces the integrated rate law. d [A] = - k d t [A] • At t = 0, [A] = [A]0 [A] = [A]0 e- k t