Chapter 13: Kinetics: Mechanisms and Rates of Chemical Reactions

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Way to determine rate of overall chemical reaction

Determined by rates of elementary reactions

Rate determining step

Elementary rxn that proceeds slower than any of other steps in mechanism. Governs rate of overall chem rxn.

kinetics

study of rates of chem rxns

kinetic units

M/s-1

The reason stoichiometry isn't used for rate law for a reaction.

because orders must be determined experimentally

Cases where stoichiometry is acceptable to determine rate law.

Single elementary steps and rate limiting steps.

Three concepts of reaction mechanisms and rate laws.

. Mechanism is one or more elementary reaction that describes how chem reaction occurs
sum of individual steps of mechanism gives balanced stoichiometric chem equation
rate law predicted by mechanism is same as experimental rate law.

Units for zero order

Ms-1

units for first order

s-1

units for second order

M-1s-1

specific heat of water?

4.184 C

(5/9)(f-32)

F to C

concentration reactant at the beginning, concentration remaining at time t, and rate constant.

In the Order reaction equations what does [A]o, [A], and kt stand for?

first order

the linear order

ln([A]o/[A])=kt

first order reactant eqn

Half life

amount of time required for half the amount of reactant to be consumed

the original concentration, [A]o

In first order reactions, what is half life independent of?

t(1/2)=ln2/k

WHAT'S HALF LIFE FORMULA?

reciprocal of concentration varies linearly with time

second order reaction graph

concentration varies linearly with time

zero order

By examining how concentration changes

how can rate laws be determined?

unimolecular fragmentation

energy of products is always higher than that of reactants

unimolecular rearrangement

the energy always rises initially, but as bond forms, energy decreases.

0.0821, 8.314

the two "R" constants

reaction mechanism

Sequence of molecular events

molecular event during chem rxn with 1-3 reactants

Elementary reactions

Most common elementary reaction. Collision of two reactants

bimolecular reaction

unimolecular reaction

Elementary reaction where a single molecule breaks into two pieces and rearranges into a new isomer

termolecular reaction

Elementary reaction where three chem species collide simultaneously. Very rare.

Chemical species produced in early step of a mechanism and consumed in a later step. Never appears in overall reaction.

Intermediates

molecular events/time

Define rate of reactions

Rate determining step

elementary rxn that procedes more slowly than any other step in mechanism. Governs overall chem rxn.

kinetics

study of rates of chem rxns.

units of kinteics

Ms-1

unimolecular rxns slow down

When less reactant molecules remain.

rate=k[A]x[B]y

rate law skeleton

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