AP Chemistry
Kinetics Notes
Plotting the concentration of a chemical in a reaction as a function of time is called a Kinetic Curve
or
Concentration vs. Time Curve
Calculate the slope at a given time by drawing a tangent at that point and calculating the slope of the line.
This is the derivative of the function at that point
Always use a positive value for rate
Rate =
Δ
C
products
/
Δ
t
Rate = 
Δ
C
reactants
/
Δ
t
Once the rate of one component is determined, others can be determined using stoichiometric ratios.
Units: mol/Ls or mol L
1
s
1
Reaction Rate Factors
1.
Concentration of reactants
2.
Temperature (Increasing temperature increases the reaction rates)
3.
Catalyst (Substance that participates but is not changed by the reaction.
It is not included in
the balanced equation
The general rate of reaction is obtained by dividing the rate of disappearance of a reactant or the rate of
formation of a product by the stoichiometric coefficient of that reactant or product in the balanced
chemical equation.
For equation aA
+ bB
→
cC
+
dD
The
general rate of reaction
is:
Rate = (1/a)
Δ
[A]/
Δ
t = (1/b)
Δ
[B]/
Δ
t = (1/c)
Δ
[C]/
Δ
t = (1/d)
Δ
[D]/
Δ
t
This represents the average rate of a reaction over a time interval, as the rate is generally greater when the
concentration of reactant(s) is greater.
Details
1.
Concentration
Expressed in the rate law
Rate = k[A]
x
[B]
y
[C]
z
k = rate constant
Exponents are usually small whole numbers but may be negative or rational fractions
They are
NOT
stoichiometric coefficients.
The rate law must be determined experimentally.
There is no theoretical way to predict
exponents.
The rate law is determined by taking the ratios of experimental results on a reaction such that one or more
of the concentrations cancel out leaving one to be determined
Ex:
Rate
2
=
k[.1]
x
[.2]
y
Rate
1
k[.05]
x
[.2]
y
This is sort of a process of elimination
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View Full DocumentAfter the exponents are determined, k may be determined from any of the reactions (see section in text for
examples)
Order of the rate law
Either:
1.
refers to the individual exponents of each component
Or
2.
refers to the sum of all of them for the overall reaction
The units of the rate constant k vary with the order of the rate law, however they must be such that the
overall rate is given in units of concentration per unit time.
If the concentration of a component has no effect on the reaction rate (i.e. zeroth order) it is not included
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 Fall '10
 Feebeck
 Reaction, Kinetics, Chemical reaction, Elementary Reactions

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