Chemical Kinetics

Speed =

distance/time

Reaction rate =

∆[A] / ∆t

∆[A] = change in concentration of A

∆t = change in time

Rate = k[A]^m[B]ⁿ

k = rate constant

[A] and [B] = concentration of the reactants

m and n = reaction orders

increase temp

increase rate constant and increase reaction rate

decrease Ea/activation energy

increase rate constant and increase reaction rate

increase reactants concentration

no effect on rate constant but increases reaction rate

rate of radioactive decay is

first order

Zero order

Rate = k[A]⁰

M•s-1

first order

Rate = k[A]¹

s^-1

second order

Rate = k[A]2

Rate = k[A][B] or k[A]² or k[B]²

M^-1•s^-1

integrated rate law zero order

[A]_t = -kt + [A]₀

slope = -k

[A]t = concentration of A at the time of

interest (M)

k = rate constant (M•s-1)

t = time (s)

[A]0 = concentration of A at time = 0 (M)

integrated rate law first order

ln[A]_t = -kt + ln[A]₀

slope = -k

second order integrated rate law

1/[A]_t = kt + 1/[A]₀

summary of integrated rate laws

Intermediate IRS

Intermediates are products first and Reactans Second

Catalyst CARP

Catalysts Are Reactants first and Products second

Arrhenius equation

k = Ae ^-Ea/RT

k = rate constant

A = frequency factor

e = Euler's number (e ≈ 2.72)

Ea = activation energy

R = universal gas constant

T = temperature (K)

high temp

increase k and increase reaction rate

low temp

decrease k and decrease reaction rate

low Ea (activation energy)

increase in k and increase in reaction rate

high Ea

decrease k and decreased reaction rate

zero order half life

t_1/2 = [A]₀ / 2k

t1⁄2 = half-life

[A]0 = concentration of A at time = 0

k = rate constant (M•s-1)

first order half life

t_1/2 = 0.693/k

k = rate constant s^-1

second order half life

t_1/2 = 1/k[A]₀

k = rate constant M^-1x S^-1

zero order reaction: as conc. decreases

half life decreases

1st order reaction

half life is independent of concentration

second order reaction as conc. decreases

half life increases