• The last page contains a list of constants and equations and a periodic table...you may remove this page for ease of use.
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• I have included two extra credit problems (5 points each) at the end...give them a try if you have time.

The decomposition of ozone may occur through the two-step mechanism shown:

Step #1 O₃ ® O₂ + O
Step #2 O₃ + O ® 2O₂

The oxygen atom is considered to be a(n)

a.) reactant
b.) product
c.) catalyst
d.) reaction intermediate
e.) activated complex

2.) The following data were obtained for the reaction of NO with O₂. Concentrations are in molecules/cm³ and rates are in molecules/cm³·s.

Which of the following is the correct rate law?

a.) Rate = k[NO][O₂]
b.) Rate = k[NO][O₂]²
c.) Rate = k[NO]²[O₂]
d.) Rate = k[NO]²
e.) Rate = k[NO]²[O₂]²

3.) For the following reaction...

H₂O₂ + 3I^-1 + 2H⁺¹ ® I₃^-1 + 2H₂O

...the experimentally determined rate law is

Rate = k[H₂O₂][I^-1]

Two mechanisms are proposed for this reaction (both mechanisms do add up to the overall reaction).

Which of the following describes a potentially correct mechanism?

a.) Mechanism I, if the first step is the rate-determining step.
b.) Mechanism I, if the second step is the rate-determining step.
c.) Mechanism II, if the first step is the rate-determining step.
d.) Mechanism II, if the second step is the rate-determining step.
e.) None of the above could be correct.

4.) The reaction quotient, Q, for a system is 7.2 x 10². If the equilibrium constant for the system is 36, what will happen as equilibrium is approached?

a.) There will be a net gain in product.
b.) There will be a net gain in reactant.
c.) There will be a net gain in both product and reactant.
d.) There will be no net gain in either product or reactant.
e.) The equilibrium constant will decrease until it equals the reaction quotient.

5.) Equilibrium is reached in chemical reactions when:

a.) the rates of the forward and reverse reactions become equal.
b.) the concentrations of reactants and products become equal.
c.) the temperature shows a sharp rise.
d.) all chemical reactions stop.
e.) the forward reaction stops.

6.) The bicarbonate ion, HCO₃^-1, is amphoteric...the conjugate acid and conjugate base of HCO₃^-1 are, respectively:

a.) H₃O⁺¹ and OH^-1
b.) H₃O⁺¹ and CO₃^-2
c.) H₂CO₃ and OH^-1
d.) H₂CO₃ and CO₃^-2
e.) CO₃^-2 and OH^-1

7.) In deciding which of two acids is stronger, one must know:

a.) the concentration of each acid solution.
b.) the pH of each acid solution.
c.) the K_a of each acid.
d.) all of the above
e.) both a and c must be known

8.) (6 points) Calculate the pH and pOH of a 8.2 x 10^-2 M HClO₄(aq) (perchloric acid) solution.

9.) (10 points) For the reaction...

A <===>B

...the following reaction coordinate diagram is drawn.

a.) Indicate which number on the chart corresponds to which quantity.

E_a of forward reaction 3

E_a of reverse reaction 2

b.) Which reaction (forward or reverse) will have the higher rate constant? (Circle one.)

c.) Is the forward reaction (A ® B) exothermic or endothermic? (Circle one.)

10.) (10 points) Consider the following system at equilibrium:

For each of the following pairs of changes, circle the change that will shift the equilibrium to the right.

11.) (10 points) When ethyl chloride, CH₃CH₂Cl, is dissolved in 1.0 M NaOH, it is converted into ethanol, CH₃CH₂OH, by the reaction

CH₃CH₂Cl + OH^-1 ® CH₃CH₂OH + Cl^-1

At 25°C the (first order) rate constant is 1.0 x 10^-3 s^-1. If the activation energy is 100.0 kJ/mol, what will the rate constant be at 40°C?

12.) (13 points) The decomposition of NO₂ is a very slow process.

2NO₂ ® 2NO + O₂

The rate constant for this reaction is 2.80 x 10^-10 L/mol·s at 25°C. If 3.00 moles of NO₂ is placed in a 2.00 L flask at 25°C, in 75.5 years there will be 1.50 moles of NO₂ left in the flask. What is the order of the reaction with respect to NO₂? (3 points will buy you a hint...)

13.) (15 points) Bromine chloride (BrCl), a reddish gas with properties similar to those of chlorine gas, may eventually replace chlorine as a water disinfectant. It is formed by the reaction of chlorine and bromine gases. 100.0 g of Cl₂ and 100.0 g of Br₂ are placed in a 5.00 L reaction flask and allowed to reach equilibrium at a certain temperature.

Cl₂(g) + Br₂(g) <===> 2BrCl(g)

The equilibrium constant for this reaction is 4.7 x 10^-2. What are the concentrations of Cl₂, Br₂, and BrCl at equilibrium?

14.) (15 points) What is the pH of a solution made by mixing 100 mL of 1.0 M hydrofluoric acid (HF) and 100 mL of 1.0 M hydrocyanic acid (HCN)?

K_a for HF = 7.2 x 10^-4, K_a for HCN = 6.2 x 10^-10.

15.) Consider the reaction

A(g) + B(g) C(g)

for which K = 1.30 x 10². Assume that 0.406 mol C(g) is placed in the cylinder represented below. The temperature is 300.0 K, and the barometric pressure on the piston (which is assumed to be massless and frictionless) is constant at 1.00 atm. The original volume (before the 0.406 mol C(g) begins to decompose) is 10.00 L. What is the volume in the cylinder at equilibrium? (aka Marathon Problem from Chapter 13.)

16.) Most reactions occur by a series of steps. The energy profile for a certain reaction that proceeds by a two-step mechanism is...

On the energy profile, indicate (i.e. label with the corresponding letter)

a.) the positions of reactants and products

b.) the activation energy for the overall reaction

d.) Which point on the plot represents the energy of the intermediate in the two-step reaction?

Which step in the mechanism for this reaction is rate determining, the first or second step? (Circle one.)

Integrated Rate Laws:
ln[A] = -kt + ln[A]₀
1/[A] = kt + 1/[A]₀
[A] = -kt + [A]₀

Half-life expressions:
t_1/2 = [A]₀/2k (zeroth order)
t_1/2 = 0.693/k (first order)
t_1/2 = 1/k[A]₀ (second order)

Arrhenius Equation:
k = Ae^-Ea/RT
ln(k) = -E_a/RT + ln(A)
ln(k₁/k₂) = E_a/R x (1/T₂ - 1/T₁)

R = 0.08206 L·atm/mol·K
= 8.3145 J/K·mol

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