Kinetics- Partial Notes

BrO Br - +6H +→ 3Br 2 + 3H 2 O Find the rate law and calculate k Experime nt [BrO 3 - ] [Br - ][H + ]Initial Rate Mol/L Mol/L s * * * *10 -3

The C-14 decay rate of wood obtained from a live tree is.260 disintegration per second per gram of sample A of a wood from a site. C-14 decay rate is.186 disintegration per second per gram. How old is the sample of tree if the half life is 5730 years?

Second Order Reaction The rate of a second order reaction depends on reactant concentration rate to the second power or on the concentrations of two different reactants, each raised to the first power. Rate= - d[A] = k[A] 2 dt

Integrated Form 1 = 1 + kt [A] [A] 0 Plot of 1/[A] vs t gives a straight line with slope equal to k

Zero Order Reactions Reaction rate does not change with a change in reactant concentrations rate= -d[A] = k [A] 0 = k Zero order reactions are most often encountered when an enzyme on a metal surface is required for the reaction to occur. dt

Integrated rate= -d [A] = k [A] 0 [A] 0 = -[A] = kt Plot of [A] vs t gives straight line with slope equal to zero. dt

Reaction Mechanism A reaction mechanism is a description of how a reaction occurs. It is usually expressed as a series of equations Each equation is called an elementary step.

Elementary Steps Unimolecular- involves one molecule Bimolecular- involves two molecules* Termolecular- involves three molecules* * can be the same or different molecules

Rate Laws and Elementary Steps The rate law for an overall reaction is determined by the experiment. The rate law for the elementary step can be determined by inspection A unimolecular elementary step follows a first order rate law A bimolecular elementary step follows a second order rate law etc…

Rate Determining Step The slowest step in a reaction mechanism A reaction can proceed no faster than the rate of its slowest step.

Mechanisms must satisfy two requirements 1. The sum of the elementary steps must give the overall balanced equation for the reaction 2. The rate law for the rate determining step must agree with the experimentally determined rate law

In general, Mechanisms….. are our best guess as to how a reaction proceeds can never be proven to be correct can be eliminated by experimental consideration