Rates
What are the four ways to write a rate expression for the following equation?
CH4 + 2O2 -> CO2 + 2H2O
Rate = -Δ[CH4]/Δt = -Δ1/2[O2]/Δt = Δ[CO2]/Δt = Δ1/2[H2O]/Δt
the order of a reaction with this rate constant: k=0.88 s-1?
First Order
What letter is used to denote the fraction of collisions with the proper orientation? How do you measure it (what is the formula)?
p = # collisions with proper orientation / total collisions
Describe the initial rates method to determine reaction order.
Experimenters change one reagent at a time with all other factors constant and collect the initial rate. Then using the change in concentration compared to the change in rate, the order of a specific reactant can be determined.
1. Zero order means increasing the reactant _______.
2. Doubling the reactant concentration will ______ the rate for a first order reactant.
3. Second order means doubling the reactant will ______ the rate.
1. ...has no effect on the rate of the reaction
2. double
3. quadruple
How quickly is AB formed if B disappears at a rate of 0.6 mol/L*sec?
A + B -> 2AB
1.2 mol/L*sec
What is the overall order of the following rate law? What would the units of k be?
Rate = [A]2[B]2[C]2
order = 6
k -> s-1M-5
Collision theory dictates that all molecules are this 3D shape
What is a sphere?
Name four ways or methods used to experimentally determine the order of a reaction.
possible answers: graphical method, integrated rate laws, initial rates, flooding / isolation method; UV spectrophotometry, quenching, titration, take aliquots to determine how much of a specific reactant or product present
True or False: The rate of a reaction will stay constant over time.
False
Write a balanced equation for the following rate expression:
Rate = -ΔC6H5CH3/Δt = -Δ1/9O2/Δt = Δ1/7CO2/Δt = Δ1/4H2O/Δt
C6H5CH3 + 9O2 -> 7CO2 + 4H2O
What is the rate constant of a reaction that is second order with respect to H2SO4 and has an initial rate of 0.57 M/s in 2.0 M H2SO4?
k = 0.14 s-1M-1
The activation energy of a chemical reaction is 100 kJ/mol and its A factor is 10 M-1s-1. Find the rate constant of this equation at a temperature of 300 K.
3.8341*10-17 M-1s-1
The reaction is second order (can tell from units of A); Make sure to convert kJ to J for this equation
In an experiment, a chemist begins with .54 M concentration of HCl. After 20 seconds, through titration, it is determined that the concentration of HCl is 0.30 M. Using the following equation, what is the average rate of change for this reaction?
HCl + NaOCH3 -> CH3OH + NaCl
1.2 x 10-2 M/sec
What are three things that affect the rate of a reaction?
Temperature, concentration, species involved, catalysis, etc
Use the following equation to answer the question:
C3H8 + 5O2 -> 3CO2 + 4H2O
If O2 is decreasing at a rate of 0.54 Mol/L*sec, what is the rate of the formation of CO2?
0.324
What is the half-life of a first order reaction with an initial concentration of A of 2.2 M, if k= 0.69 s-1?
2A + B -> C
rate = k[A]
.50 (don't need to use initial concentration for first order half life)
At a temperature of 600 K, the rate constant of a chemical reaction is 2.75*10-8 M-1s-1. When the temperature is increased to 800K, the rate constant for the same reaction is 1.95*10-7M-1s-1. What is the activation energy of this reaction?
Ea = ~39085 J*mol-1
Consider the following kinetic data collected at the very beginning of a reaction:
Run # Initial [A] Initial [B] Initial Rate Rxn
(mol/L) (mol/L) (mol/L-s)
-------------------------------------------------------
1 0.10 0.10 0.0090
2 0.20 0.10 0.036
3 0.10 0.20 0.018
Which of the following is an appropriate expression for the rate law and rate constant?
a) Rate = k[A]2[B]; k = 9.0 L2/mol2-s
b) Rate = k[A]2[B]2; k = 0.9 L2/mol2-s
c) Rate = k[A]4[B]2; k = 9000 L / mol-s
d) Rate = k[A][B]; k = 0.9 L / mol-s
A
What are the key components of collision theory (how must particles collide in order to react?)
Particles must collide with a certain amount of energy and the correct orientation.
For the oxidation of ammonia
4NH3 + 3O2 -> 2N2 + 6H2O
it was found that the rate of the formation of N2 was 0.27 mol/L*sec. At what rate is ammonia being consumed?
0.54 mol/L*sec
At what concentration of CH4 is the rate of the reaction 1.5 M/s if k = .60 s-1 and CH4 is the only species involved in the rate equation (everything else is zero order)?
2.5 M
It takes about 3.0 minutes to cook a hard-boiled egg in Los Angeles, but at the higher altitude of Denver, where water boils at 92°C, the cooking time is 4.5 minutes. Use this information to estimate the activation energy for the coagulation of egg albumin protein.
Ea = 57.4 kJ/mol
(make sure to convert degrees C to K)
Determine the rate-law expression for the reaction below:
2A + B2 + C --> A2B + BC
Run # Init. rate [A] [B2] [C]
-----------------------------------------------------
1 1.6 x 106 1.2 M 1.0 x 10-2 M 1.0 M
2 1.6 x 106 2.4 M 1.0 x 10-2 M 1.0 M
3 3.2 x 106 1.2 M 2.0 x 10-2 M 1.0 M
4 6.4 x 106 1.2 M 1.0 x 10-2 M 2.0 M
Rate = 1.6x108[B2][C]2
The order given the half-life T1/2=1/(k*[A]o)
What is second order?