
Factors that affect reaction rates o Physical state of the reactants, [ ] of the reactants, temperature at which the reaction occurs and presence of a catalyst

Reaction rates and determination of average rate of appearance products and disappearance of reactants (depends on coefficients in balanced equation, think Stoichiometry).

How rate of a reaction changes over time and determining instantaneous rate

Using concentrations of reactants to determine orders for individual reactant molecules or ions.

Determining overall order for a reaction

Determining value of the rate constant, k, and the units of k. o If overall order is zero order, k has units of Ms -1 , mol/L s, or M/s o If overall order is 1 st order, k has units of s -1 or 1/s o If overall order is 2 nd order, k has units of M -1 s -1 , L/mol s, or 1/M s o If overall order is 3 rd order, k has units of M -2 s -1 , L 2 /mol 2 s or 1/M 2 s

Determining the rate of a reaction from initial [ ]s and k.

Integrated rate laws

Zero Order [A]
0
– [A] t
= kt Half-life equation t ½ = [A]
0
/2k [ ] vs. t is a straight line graph Slope = -k o 1 st Order ln[A] t
= -kt + ln[A]
0
Half-life equation: t
½
= ln 2/k ln [ ] vs. t is a straight line graph Slope = -k o 2 nd Order 1/[A] t
= kt + 1/[A]
0
Half-life equation: t
½
= 1/k[A]
0
1/[ ] vs. t is a straight line graph Slope = k

Temperature and Rate – collision model and orientation factors

Activation energy (E a
) – in kJ/mol usually – from reactants to the top of the curve o Activated complex(s) or transition state(s) – top of the curve o Intermediate(s) – bottom of the dip, but not the reactants or the products o 
E – difference between the energy of the reactants and the products
 If products are at a higher energy than reactants – exothermic or exergonic reaction
 If reactants are at a higher energy than products – endothermic or endergonic reaction

High E a
= slower rate of reaction; low E a
= faster rate of reaction

Arrhenius equation : k = Ae -Ea/RT k is rate constant; A is frequency factor; e is the inverse ln;
R = 8.314 J/mol K or 0.008314 kJ/mol K; and T is Kelvin temperature; Slope = -E a
/R o Arrhenius equation could also be written as ln k= -Ea/RT + ln A o If given two different temperatures or two different rates, use ln(k
1
/k
2
) = Ea/R(1/T
2
-1/T
1
)

Reaction Mechanisms – elementary reactions or processes are just individual reactions (reactants  products)

Molecularity – one reactant = unimolecular, two reactants = bimolecular, and three reactants = trimolecular o If you have a coefficient of 2 or 3 that does affect the molecularity!

Multistep mechanisms – the rate-determining step is also the slow step. The rate law must be written from the rate-determining step with each raised to the power of its coefficient.

The rate law cannot include an intermediate. If the slow step includes an intermediate, you must use the fast equilibrium step and solve it for the intermediate and then substitute back into the rate-determining step for the intermediate. o If you have an equilibrium, then rate law for forward reaction = rate law for reverse reaction

Catalysis – decreases Ea for both the forward and reverse reactions. Does not change the

E for the overall reaction. A catalyst can be recovered unchanged at the end of a reaction. It will be in the reactants of an early step of the reaction and in the products of a later step versus an intermediate is first produced and then later consumed.