Name:___________________________
Physical Chemistry Exam 3
Chem 352/361
Part I: Multiple Choice (10 problems x 2 points each = 20 points)
1. Which of the following is not assumed by kinetic molecular theory?
a. All molecules at a given temperature travel at the same speed.
b. Gases consist of molecules in constant, random motion.
c. Molecules interact only through brief, elastic collisions.
d. The size of a gas molecule is negligible in comparison to its container.
2. Which integral is evaluated to find the average speed of a molecule?
∞
a. ∫𝟎 𝒇(𝒗)𝒅𝒗
∞
b. ∫−∞ 𝒇(𝒗)𝒅𝒗
∞
c. ∫𝟎 𝒗𝟐 𝒇(𝒗)𝒅𝒗
∞
d. ∫−∞ 𝒗𝒇(𝒗)𝒅𝒗
3. Which of the following is true of rate laws?
a. The rate of any reaction can be written as 𝜐 = 𝑘[𝐴]𝑎 [𝐵]𝑏 ⋯
b. The rate law of the reaction A + B  C could possibly be
𝜐 = 𝑘[𝐴]2
c. The rate law of the reaction 2 A  B must be 𝜐 = 𝑘[𝐴]2
d. The rate law of the reaction 2 A  B is 𝜐 = 𝑘[𝐴]2 only if the reaction is
elementary.
4. Which plot would be used to determine if a reaction is 0th order in [A]?
a. ln([A]) vs. t
b. [A]-2 vs. t
c. [A] vs. t
d. [A]-1 vs. t
5. Which plot would be used to determine if a reaction displays Arrhenius
behavior?
a. υ vs. t
b. U vs. ξ
c. log(Y/(1-Y)) vs. log(p)
d. ln(k) vs. 1/T
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6. Given a reaction mechanism of A  I  P, what is the assumption that
d[I]/dt = 0 called?
a. Michaelis-Menten kinetics
b. Steady-state approximation
c. Pre-equilibrium
d. Pre-dissociation
7. Which of the following plots demonstrates the expected changes in a
Lineweaver-Burke plot upon the addition of a competitive inhibitor, I?
a.
b.
c.
d.
8. The cooperative nature of the binding of oxygen to hemoglobin can be
explained by a model that…
a. …treats hemoglobin like it treats myoglobin
b. …utilizes the Hill equation with n = 1
c. ...allows O2 to bind to two different conformations of hemoglobin
d. …treats CO as a competitive inhibitor
9. The rate law for a reaction following a Lindemann-Hinshelwood mechanism
𝑘 𝑘 [𝐴]2
2
is 𝜐 = 𝑘 ′1[𝐴]+𝑘
. The reaction will likely appear first-order if…
a.
b.
c.
d.
1
2
…most of the A* that is formed quickly deactivates to A.
…a radical initiator is present.
…the reaction is performed at a low partial pressure of A.
…the rate-determining step is the collision of two A molecules
10. Which statement about the reaction A + BC  AB + C is true if it has an
attractive potential energy surface?
a. The transition state most closely resembles a BC molecule with an
approaching A atom.
b. The transition state most closely resembles an AB molecule with a
departing C atom.
c. At the transition state, RAB = RBC.
d. The addition of vibrational energy to the BC bond will not affect the
probability of reaction.
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Part II: Short questions (5 problems x 6 points each = 30 points)
Choose 5 of the following 6 questions and answer them. Make sure you clearly show
which problem you are skipping. (It’s OK to make attempts on each one, but Chris is
only going to grade five of them.)
1. Given the Maxwell distribution of speeds (Chris will identify this for you for a
2𝑅𝑇
price of 1 point), find the expression for the most probable speed, 𝑐 ∗ = √
3
𝑀
2. Calculate the collision cross-section, collision frequency, and mean free path
of H2 at 500 K, given a density of 0.0446 mol/L. Treat H2 as a sphere with a
radius of 0.20 nm. (2 points each)
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3. The reaction A  B is monitored by spectroscopically measuring the
concentration of A as it decreases from an initial concentration of 1.0 M. The
half-life is measured to be 3.6 minutes, and [A] = 0.25 when t = 10.8 minutes.
Determine if the reaction is 0th, 1st, or 2nd order in A (2 points), and calculate
the rate constant. (4 points)
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4. The Lineweaver-Burke plot below describes the rate of hydrolysis of
N-glutaryl-L-phenylalanine-p-nitroanilide (catalyzed by α-chymotrypsin) as
a function of substrate concentration. Use it to calculate Vmax and KM.
0.5
1/vo(106 min/M)
0.45
y = 0.9444x + 0.076
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
-0.2
-0.1
0
0.1
0.2
1/[S] (1/M)
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0.3
0.4
0.5
5. Use collision theory to calculate the rate constant for the reaction below at
650 K.
H2 (g) + I2 (g)  2 HI (g)
a. Use a collision cross-section of 0.36 nm2 and an activation energy of
171 kJ/mol. The mass of H2 is 3.32 x 10-27 kg and the mass of I2 is 4.21
x 10-25 kg. Assume that all collisions with sufficient energy will
lead to product formation. (4 points)
b. If the true reaction rate constant is measured to be 1.6 x 10-4 M-1 s-1,
what is the steric factor? (2 point)
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6. A first order reaction has a half-life of 25 hours at 300 K and a half-life of 10
hours at 750 K. Determine its activation energy.
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