Chemical Kinetics

1. Chemical Kinetics • Reaction rate - the change in concentration of reactant or product per unit time.

2. Factors Affecting Rates • Temperature • Concentration of reactants • Particle size • Presence of a catalyst

3. Rates • Average rates - the difference in concentration over a set amount of time. Table 12.2 • Instantaneous rates - calculated from the slope of the line tangent to the curve at a certain point.

4. Reaction rates • Rates are not constant. • Rates vary with time because concentrations vary with time.

5. Rate Laws • Rate = k[A]n[B]m[C]p • k = rate constant • n,m,p = order ; must be determined by experiment.

6. Differential rate law • Expresses how a rate depends on concentration. • Often this is just called the rate law.

7. Integrated rate law • Expresses how the concentration depends on time.

8. Reaction Mechanism • The series of elementary steps by which a reaction occurs. • An elementary step is a step whose rate law can be determined from its molecularity.

9. Molecularity • The number of species that must collide to produce the reaction in that step. • Unimolecular involves one molecule. • Bimolecular and termolecular involve 2 and 3 species respectively

10. Intermediate • A species that is neither a reactant or a product. This species is produced and consumed in the reaction.

11. Rate Determining Step • This is the slowest step of the mechanism. The reaction can only proceed as fast as this rate determining step will allow.

12. Requirements of Mechanisms • The sum of the elementary steps must give the overall balanced equation. • The mechanism must agree with the experimentally determined rate law. The rate determining step.

13. Collision model for kinetics • Reactant molecules must collide in order to react. • Concentration • Particle size • Temperature • Molecular orientation

14. Requirements for reaction • The collision energy must equal or exceed the activation energy. • The orientation of the reactants must allow the formation of new bonds.