Chem 102 Exam 2 Review
Rate Laws
•
A rate law shows the relationship between the reaction rate and the concentrations of the
reactants
•
The exponents tell the order of the reaction with respect to each reactant
•
The overall reaction order can be found by adding the exponents on the reactants in the
rate law
•
Generally, as the temperature increases, so does the reaction rate
•
This is because k (rate constant) is temperature dependent
Arrhenius Equation
•
Arrhenius developed a mathematical relationship between R and E
a
K = Ae
Ea/RT
where A is the frequency factor, a number that represents the
likelihood that collisions would occur with the proper orientation for reaction. (Temperature
doesn’t affect the activation energy (E
a
))
•
Taking the natural logarithm of both sides, the equation becomes
lnk=Ea (1/RT) + lnA
y = mx + b
Therefore, if k is determined experimentally at several temperatures, Ea can be calculated from
the slope of a plot of lnk vs. 1/T
Reaction Mechanisms
•
The molecularity of a process tells how many molecules are involved in the process
•
In a multistep process, one of the steps will be slower than all others
•
The overall reaction cannot occur faster than this slowest, ratedetermining step
Concept of Equilibrium
•
Chemical equilibrium occurs when a reaction and its reverse reaction proceed at the same
rate
•
As a system approaches equilibrium, both the forward and reverse reactions are occurring
•
Once equilibrium is achieved, the amount of each reactant and product remains constant
Properties of Equilibrium
Equilibrium systems are
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Dynamic (in constant motion)
•
Reversible
•
Can be approached from either direction
Depicting Equilibrium
In a system at equilibrium, both the forward and reverse reactions are being carried out; as a result, we
write its equation with a double arrow
Rate Constants
•
K is large for high reaction rates and is dependent on temperature
•
Units of k vary with reaction order
•
Rate = k [A]
n
[B]
m
aA + bB→ cC + dD
•
Reaction orders, n and m, may be independent of stoichiometric coefficients, a and b
•
Overall reaction order is n+m
Temperature and Rate
•
Generally, as the temperature increases, so does the reaction rate
•
This is because k is temperature dependent
HalfLife
•
Halflife is defined as the time required for onehalf of a reactant to react
•
Note: For a 1
st
order process, the halflife does NOT depend on the initial concentration
Reaction Mechanisms
•
The sequence of events that describes the actual process by which reactants become
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 Spring '08
 Williamson
 Chemistry, Equilibrium, pH, Reaction, ea, Equilibrium Equilibrium systems

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