General Kinetics Laws
Does Temperature have any effect on the activation energy of a reaction?
No, it simply raises the rate of reaction
For the following chemical reaction:
HClO(aq) + H2O(l) -> ClO-(aq) + H3O+(aq)
Write an equation that compares the average rate of disappearance of Hypochlorous Acid to the average rate of appearance of the Hydronium cation.
-d[HClO]/dt = d[H3O+]/dt
Consider the generalized reaction A -> B
Given the following experimental information, what is the order of reaction in A for this reaction?
Experiment # | [A] | Rate
1 |1.5M| 3.0 M/s
2 |12.0M| 24.0 M/s
24.0/3.0= (12.0/1.5)x
8 = (8)x
x = 1
The reaction is first order in A
For a generalized reaction A -> B which is first order in A & has a rate constant of 0.50 1/s, with an initial concentration of 100.0 g/L. At what time (in seconds) will the concentration be decreased by 65%?
100% - 65% = 45%
(45/100)*100.0 g = 45 g
ln(45) = -(0.50/s)t +ln(100)
(ln(45/100.0))s/(-0.50) = t
t = 1.6 seconds
Do very fast steps have an effect on the on the rate law?
No, only the slow step, the rate determining step, will affect the rate law
Assume you have two solid samples of thermite in different reaction vessels. In one vessel, the thermite is contained under normal conditions & is ignited, burning at a normal rate. However in the other reaction vessel, the concentration of oxygen is highly increased, & the burning reaction is violent. Why?
Because the reaction is dependent on oxygen's concentration, & as such will proceed rapidly when oxygen is present in high concentrations.
For the following chemical reaction:
C7H16(g) + 11O2(g) -> 7CO2(g) + 8H2O(g)
If the rate of disappearance of Oxygen gas is determined to be 1.52*10-2 M/s, what is the rate of appearance of water vapor?
1.11*10-2 M/s
For a generalized reaction A + B -> C
If the reaction is 3/2 order in A & 7/3 order in B, what is the units for k in the rate law?
Rate = (M/s)/((M3/2)(M7/3)) -> (6+14-6)/6 = M-14/6
k units: 1/(M7/3)(s)
In a farm, there is runoff of fertilizer into a watershed. The concentration of fertilizer in the water shed is 5.0 * 10^-4 M, with a rate constant of 0.0125 1/yr. Suppose the fertilizer is depleted from the water shed following 1st order kinetics, how long (in years) will it take for half of the fertilizer to be depleted from the water shed?
ln(2)yr/0.0125 = 55.45 years
Consider the following Mechanism:
NO2 + NO2 -> NO3 + NO (slow)
NO3 + CO -> NO2 + CO2 (fast)
What is the overall equation?
What is the rate law?
Overall: NO2 + CO -> NO + CO2
Rate Law: Rate = k1[NO2]2
Is it possible to determine if a reaction is rapid or slow if only Change in Enthalpy is known? What about if the activation energy is known & why?
If only change in enthalpy is given, rate of reaction cannot be determined because the reaction rate is not directly dependent on thermodynamic quantities. However, rate of reaction is dependent on activation energy because the more energy that is required to initiate a reaction, the slower the reaction will be.
For a generalized reaction: A + B -> C
Assuming A is being consumed at a rate of 1.5 * 10-2 M/s, B is being consumed at a rate of 3.5 * 10-2 M/s, & C is being produced at a rate of 1.0 * 10-2 M/s. What is the most simplified stoichiometric form of this equation?
(3/2(A) + 7/2(B) -> 1(C))*2
3A + 7B -> 2C
For a generalized reaction A -> B
The reaction is first order in A. Find the rate constant if the reaction rate is 2.5 * 10-2 M/s when the concentration of A is 1.25 * 10-2 M.
k = (2.5)/(1.25) = 2
For the following reaction
NO2(g) -> (1/2)O2(g) + NO(g)
Assuming it is second order overall and the initial concentration is 0.0250 M with k = 0.543 M-1s-1, what will the concentration be after an hour and a half?
Consider the generalized overall reaction:
2L + M -> O + R
It's reaction pathway is described with the following system of equations:
L + L = P (fast)
M + P -> Q + R (slow)
Q -> O (fast)
Assuming P in an unstable intermediate, what is the overall rate law?
If Ea for this reaction = 12.0 kJ/mol & A = 2.5, what temperature would be required for this statement to be true?
Rate2 = k[M][P]
p is unstable, must be substituted
Rate1f = Rate
When creating a fire, you often want to select smaller pieces of wood referred to as kindling to start the fire rather than large logs. In regards to kinetics, why is this the case?
Because of the physical difference between kindling and large logs, i.e. more surface area for burning
For a generalized reaction A->B, the starting concentration of A is 0.5 M. 30 seconds into the reaction, the concentration of A is 0.1 M. What is the average rate of disappearance of A?
-(0.1 - 0.5)/(30-0) = 1.3 * 10-2 M/s
For a generalized reaction A + B -> C
If it is 1/2 order in A & 2/3 order in B, what is the overall reaction order of the reaction?
7/6
1. Consider the following reaction:
2NO(g) + O2(g) -> 2NO2(g)
Determine the rate law for this reaction using the experimental data provided:
Exp. # [NO2] [O2] Rate
1 0.0235 0.0125 7.98*10-3
2 0.0235 0.0250 15.9*10-3
3 0.0470 0.0125 32.0*10-3
4 0.0470 0.0250 63.5*10-3
2. Using the rate law, determine the rate of reaction when [NO2] = 0.0750 & [O2] = 0.0200