Reaction Rates
What is the definition of reaction rate
The change in concentration of a reaction or product per unit of time
How can you find the overall order of a reaction?
Add together the exponents of reactants in the experimentally determined rate law
Or by looking at the units for k
first-order
What is the rate determining step in a multi-step reaction mechanism
the slow step
Variables that affect the rate of a reaction
Reactant concentration, temperature, presence of a catalyst, and surface area.
What are the units of k for a 5th order reaction?
k = M-4 s-1
Find k for a first-order reaction with a half life of 5.78s
k = 0.12
What is the intermediate of the following mechanism?
H₂O₂ + I⁻ → HOI + OH⁻
HOI + H₂O₂ → H⁺ + H₂O + O₂ + I⁻
HOI
If the concentration of a reactant "A" changes from 0.97M to 0.43M in 10 seconds, what is the average rate of the disappearance of A?
0.054 M/s
Create a general rate law for the following equation:
2 ClO2 + 2 OH- --> products
Rate = k[ClO2]x[OH-]y
True or False:
In the first-order reaction 2A --> B + C the time required for one-half of substance A to react is directly proportional to the quantity of A initially present
False: The time required for one half of substance A to react (t1/2) is independent of the concentration for a first order reaction
What is the difference between a catalyst and an intermediate?
Intermediate is formed and then used (found in products then reactants)
Catalyst reactant that lowers activation energy (unchanged by the reaction, found in reactants then products).
For the chemical reaction:
2Fe2O3 + C --> Fe + 3CO2
Find the rate of disappearance of Fe2O3 if the rate of CO2 formation is 0.72 M/s
rate of Fe2O3 = 0.48 M/s
If doubling the concentration of a reactant "A" quadruples the rate, what is the order of the reaction with respect to A?
second order
find [A] after 5 seconds if [A0] = 0.60 M, k = 0.80 M-1s-1
[A] = 0.176 M
In a multistep mechanism, how can you determine if the proposed individual steps are correct?
Individual steps must add together to match overall reaction. Rate law must match the experimentally observed rate law.
From the following experimental data, determine the rate order with respect to X and Y.
Experiment: [X] [Y] Initial Rate
1 0.020 0.050 1.00 x 10-5
2 0.040 0.050 2.00 x 10-5
3 0.040 0.100 4.00 x 10-5
X: first order
Y: first order
Find k from the following experimental data
[X] Rate
Experiment 1: 0.10 4.0 x 10-4 M/s
Experiment 2: 0.20 1.6 x 10-3 M/s
k = 0.04 M-1s-1
Find the activation energy (Ea) from the following experimental data
T k (s-1)
300 K 1.2 x 103
320 K 2.8 x 103
Ea = 33.9 kJ/mol
In an energy diagram, what does the top of the curve represent?
Transition state (activated complex)