AP Chemistry: Kinetics

kinetics

the study of the speed of reactions

five main factors that affect the rate of a chemical reaction

nature of the reactants, temperature, concentration of reactants, physical state of reactants, catalyst

catalyst

a substance that speeds up the rate of reaction without being consumed

activation energy

minimum amount of energy that must be supplied to the reactants in order to start the reaction

*k*

rate constant

*t*

time

*t1/2*

half-life

*m, n*

orders of reaction

orders of reaction

indicate what effect a change in concentration of a reactant species will have on the reaction rate

when a reactant is first-order, the rate ________ when the concentration doubles

doubles

when a reactant is second-order, the rate ________ when the concentration doubles

quadruples

when a reactant is zero-order, the rate ________ when the concentration doubles

does not change

integrated rate laws

laws that take account changes in the concentration of reactants and products over time

first-order integrated rate law

ln\[A\]t-ln\[A\]0=-kt

second-order integrated rate law

1/\[A\]t-1/\[A\]t0=kt

zero-order integrated rate law

\[A\]t-\[A\]0=-kt

half-life

amount of time it takes for a reactant concentration to decrease to one-half of its initial reaction

for a first-order reaction, tha half life is

constant and independent of reactant concentration

half-life equation

0\.693/k

the rate constant *k* is affected by

temperature

reaction mechanism

a sequence of reactions that describe a simpler written reaction

reactants must collide with the proper ________ for the reaction to proceed

orientation and force

reaction intermediates

chemical species that are produced and consumed during the reaction but do not appear in the overall reaction

elementary step (elementary reaction)

an individual step in a reaction mechanism

rate-determining step

the slowest step in a reaction mechanism

the rate law of the rate-determining step is

the rate of the overall reaction

bimolecular reactions

reactions that involve the collision of two chemical species

unimolecular reactions

reaction that involve the decomposition or rearrangement of a signle chemical species

termolecular reactions

reactions that involve the collision of three or more chemical species

homogeneous catalysts

catalysts that are in the same phase as the reactants

homogeneous catalysts provide

an alternative reaction pathway with a lower activation energy

heterogeneous catalyst

catalysts that are in a different phase from the reactants

heterogeneous catalysts provide

a surface for the reaction and a better orientation of one reactant

most heterogeneous catalysts are

finely divided metals

measuring _____ is essential to all kinetic experiments

time

describe a regular clock experiment

a experiment in which the solution changes color when one of the reactants disappears

what equipment is needed in a clock experiment

glassware and a thermometer

spontaneous reactions

reactions that happen but the time they happen or their speed cannot be determined

inhibitor

a substance decreasing the rate of reaction by increasing the activation energy

are concentrations of products in the rate law

no

what is the only way the values of the rate orders be determined

experimentally

what is the order of radioactive decay

first-order

molecularity

the number of moles reacting

when is the slow step's rate law not the same as the overall rate law

when it is not the first elementary step

Collision Model

the energy (for breaking bonds of reactants) comes from the kinetic energies possessed by the reacting molecules before the collision

what does the rate of reaction depend on

the number of successful collisions and these collisions provide the energy for molecules to react and form products 

is collision orientation important for both molecules and atoms

no, only molecules

which elementary step has the highest activation energy

the slow step

intermediates are found at the _____ of reaction profiles

minimum

transition states are found at the _____ of reaction profiles

maximum

the number of peaks in a reaction profile corresponds with the number of

elementary steps

transition state (activated complex)

reactive (unstable) condition of the substrate after enough energy has been absorbed to start the reaction; bonds are partially formed

equation for activation energy on a reaction profile

Activated Complex - Change in Reactants (peak - line)

equation for activation energy of the reverse reactions

Forward Activation Energy - |delta H|

equation for delta H (delta E) on a reaction profile

energy of products minus energy of reactants

reactions at which molecularity have a very low probability of occuring

termolecular

units of *k* for a zero-order reaction

M/s

units of *k* for a first-order reaction

s^-1

units of *k* for a second-order reaction

M^-1 s^-1

Arrhenius equation

k=Ae^-Ea/RT

frequency factor (A) (pre-exponential factor)

frequency and orientation of collisions

f

fraction of collisions with enough energy for a reaction to occur