• Rate or speed a chemical reaction occurs.
• Kinetic refers to the reaction rate. Does the rxn proceed rapidly enough? Is the
rxn product favored and will we get the desired products?
Average rate of reaction
• Measured by the decrease in concentration of a
reactant or an increase in concentration of a product over a time interval.
Reactants ---> Products
A à B
• Average Rate = - [A] / time
• Average Rate = [B] / time
in concentration([ ] means Molarity) / time interval
is always a + quantity
plot of concentration vs time
Instantaneous rate: at a
specific time this is the negative of the slope of a tangent line.
• 2. Initial
rate: at time = 0 this is the negative
slope of the tangent line.
Instantaneous rate at time zero.
Factors affecting reaction rates
• 1. The nature
of the reacting species
• a. Aqueous
Type of reaction requiring a specific orientation
• 2. Have
different phases or layers where the rxn occurs at the boundary of the
subdivision. Directly related to
surface area of the contact site.
• 3. Temperature
of the reactants: Reaction rate is
temperature dependent, so a Temperature is given.
• increase in
temperature, increase in rate!!
• 4. Collison
theory: The rate is proportional to the
number of molecular collisions per unit time.
Related to the concentration of
the reactants at a fixed temperature.
Calalyst: a substance that
increases the rate of a chemical reaction without itself being consumed.
• ratecatalysed> rateuncatalyzed
• 6. Energy of
activation: Ea minimum amount of energy required to
initiate a chemical reaction forming an activated complex (transition
• Arrhenius equation:
Rate Law or rate equation
• A mathmatical
equation determined experimental for the effect of concentrations of reactants
on reaction rates at constant temperature.
aA + bB --> cC + dD
Rate = k [A]a[B]b
k = rate constant for a particular rxn at a
specific temperature. Need to be able to calculate the units!!! Greater the k,
faster the reaction
[ ] = Molarity of each reactant
a, b, etc = order of reaction with respect
to each are exp. determined
Order of reaction
0 is called zero order
1 is called first order
2 is called second order
3 is called third order
Overall order = sum of
the order of rxn with respect to each reactant NOT RELATED TO COEFFICIENTS
NO + O3 à NO2 + O2 at 25oC
• 1. What is the general rate equation?
[O3] Rate = M/s
1. 1.00 3.00 .660
2. 1.00 6.00 1.32
3. 1.00 9.00 1.98
4. 2.00 9.00 7.92
Give the rate law with
the orders of rxn. What is the value of
the rate constant?
CH3CHO à CH4 + CO at 100oC
• Exp. [CH3CHO] rate = M/s
• 1. 1.75 x 10-3 2.06 x 10-11
• 2. 3.50 x 10-3 8.24 x 10-11
• 3. 7.00 x 10-3 3.30 x 10-10
the general rate law with the orders of reaction.
the rate constant.
ICL + H2 à HCl + I2 at 225 K
• Exp. [ICl] [H2]
Rate = M/s
• 1 1.5x10-3 1.5x10-3 3.7x10-7
• 2. 3.0x10-3 1.5x10-3 7.4x10-7
• 3. 3.0x10-3 4.5x10-3 2.2x10-6
rate law,Rate constant
if you have 4.5x10-3 ICl
Integrated rate equation
to the overall order of the rxn.
t1/2 time required for the
concentration of a reactant to decrease to half of the original.
1st order overall
rate equation, p. 520
• ln ([A] / [Ao]) = -kt
• half-life, p. 525
• t1/2 = 0.693 / k
2nd order overall
either one reactant that is second order or two reactants, each first order,
with the same concentration. P. 527
• 1/ [A]
– 1/ [Ao] = kt
• t1/2 = 1/ k[Ao]