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overall Reaction Mechanism
Reaction The following mechanism is proposed for a reaction: NO2(g) + NO2(g) → NO(g) + NO3(g) NO3(g) + CO(g) → NO2(g) + CO2(g) NO2(g) + CO(g) → NO(g) + CO2(g) Overall Intermediate – forms in one step of the reaction but disappears in
a following step.
following Catalyst – is used up (a reactant) in one step but forms as a
product in the later step.
product Reaction Mechanisms
Reaction Proposed mechanisms must satisfy the experimental
rate law expression.
rate Usually the rate law is related to the rate-determining
step in the reaction; the slow step in the reaction.
step Rate-determining step – the step that controls the
speed of the reaction.
speed Reaction Mechanisms
Reaction For the reaction discussed before
For NO2(g) + CO(g) → NO(g) + CO2(g) The experimental rate law is found to be: rate = k[NO2]2
The proposed mechanism was: NO2(g) + NO2(g) → NO(g) + NO3(g) NO3(g) + CO(g) → NO2(g) + CO2(g) Overall Slow step Reaction Mechanisms
Reaction The reactants in the slow step are present
The in the rate law.
in Any proposed mechanism must agree with
Any the rate law.
the Reaction Mechanism
Reaction For the overall reaction:
2 N2O5 4 NO2 + O2
The following mechanism is proposed:
N2O5 N2O4 + O
O + N2O5 N2O4 + O2
What is a possible next step in the reaction?
What The intermediate in the reaction is: A) N2O5 b. N2O4 c) O d) O2 Activation Energy
Activation Activation Energy (Ea): The potential energy barrier that
must be overcome before reactants can be converted into
products. ΔH Temperature Dependence of k
Temperature As the temperature increases what happens to the
rate of the reaction?
− RT k = Ae A – Arrhenius constant, freq. of collisions with correct
T – temp in Kelvin
R – Ideal Gas Constant in Joules (8.314 J/K-mol) The Arrhenius Equation
The A simpler way to use this is by comparing the rate constant at just
two Ea 1 1 k2
ln =− − k1
R 2 T1
T If the rate of a reaction doubles by increasing the temperature by
10°C from 298.2 K to 308.2 K, what is the activation energy of the
reaction? Energy Profile of Catalyzed Reaction
Energy polar stratospheric clouds
contain ice crystals that
catalyze reactions that
release Cl from
atmospheric chemicals Catalytic Hydrogenation
H2C=CH2 + H2 → CH3CH3...
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This note was uploaded on 09/29/2013 for the course CHM 1046 taught by Professor Staff during the Fall '08 term at FIU.
- Fall '08