Studied by 8 peoplekinetics
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
Note
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