AP CHEMISTRY –
CHAPTER 14 PRACTICE TEST: Reaction Kinetics KEY
CHEMISTRY SECTION I : NO CALCULATORS MAY BE USED WITH SECTION I
Part A
Directions: Each of the questions or incomplete statements below is followed by five suggested answers or
completions. Select the one that best answers the question.
Questions 1-2 H3AsO4 + 3I¯ + 2 H3O+ ---> H3AsO3 + I3¯ + H2O
The oxidation of iodide ions by arsenic acid in acidic aqueous solution occurs according to the
stoichiometry shown above. The experimental rate law of the reaction is: Rate = k [H3AsO4] [I¯] [H3O+]
(1) What is the order of the reaction with respect to I¯?
(A) 1
(B) 2
(C) 3
(D) 5
(E) 6
(2) According to the rate law for the reaction, an increase in the concentration of hydronium ion has what
effect on this reaction?
(A) The rate of reaction increases.
(B) The rate of reaction decreases.
(C) The value of the equilibrium constant increases. (D) The value of the equilibrium constant decreases.
(E) Neither the rate nor the value of the equilibrium constant is changed.
(3) A(g) + B(g) <===> 2 C(g)
When the concentration of substance B in the reaction above is doubled, all other factors being held
constant, it is found that the rate of the reaction remains unchanged. The most probable explanation for
this observation is that
(A) the order of the reaction with respect to substance B is 1
(B) substance B is not involved in any of the steps in the mechanism of the reaction
(C) substance B is not involved in the rate-determining step of the mechanism, but is involved in
subsequent steps
(D) substance B is probably a catalyst, and as such, its effect on the rate of the reaction does not depend
on its concentration
(E) the reactant with the smallest coefficient in the balanced equation generally has little or no effect on
the rate of the reaction.
(4) Nitramide, N2H2O2, decomposes slowly in aqueous solution. This decomposition is believed to occur
according to the reaction mechanism above. The rate law for the decomposition of nitramide that is
consistent with this mechanism is given by which of the following?
(A) Rate = k [N2H2O2]
fast
Step 1) N2H2O2 <===> N2HO2¯ + H+
(B) Rate = k [N2H2O2] [H+]
equilibrium
(C) Rate = (k [N2H2O2]) / [H+]
Step 2) N2HO2¯ ---> N2O + OH¯
(slow)
(D) Rate = (k [N2H2O2]) / [N2HO2¯]
Step 3) H+ + OH¯ ---> H2O
(fast)
(E) Rate = k [N2H2O2] [OH¯]
(5) rate = k[X]
For the reaction whose rate law is given above, a plot of which of the following is a straight line?
(A) [X] versus time (B) log [X] versus time (C) 1/[X] versus time (D) [X] versus 1/time (E) log [X] versus 1/timE
(6) The initial-rate data in the table above were
obtained for the reaction represented below. What
is the experimental rate la for the reaction?
(A) rate = k[NO] [O2]
(C) rate = k[NO]2 [O2]
(E) rate = k[NO] / [O2]
(B) rate = k[NO] [O2]2
(D) rate = k[NO]2 [O2]2
Initial
Experiment [NO]
(mol L¯1
Initial
[O2]
(mol L¯1
Initial Rate of
Formation of
NO2
(mol L¯1 s¯1)
1
0.10
0.10
2.5 x 10¯4
2
0.20
0.10
5.0 x 10¯4
3
0.20
0.40
8.0 x 10¯3
(7) (CH3)3CCl(aq) + OH¯ ---> (CH3)3COH(aq) + Cl¯
For the reaction represented above, the experimental rate law is given as follows. Rate = k [(CH3)3CCl]
If some solid sodium solid hydroxide is added to a solution that is 0.010-molar in (CH3)3CCl and 0.10molar in NaOH, which of the following is true? (Assume the temperature and volume remain constant.)
(A) Both the reaction rate and k increase.
(B) Both the reaction rate and k decrease.
(C) Both the reaction rate and k remain the same.
(D) The reaction rate increases but k remains the same.
(E) The reaction rate decreases but k remains the same.
(8) Relatively slow rates of chemical reaction are associated with which of the following?
(A) The presence of a catalyst
(B) High temperature (C) High concentration of reactants
(D) Strong bonds in reactant molecules
(E) Low activation energy
Step 1: Ce4+ + Mn2+ ---> Ce3+ + Mn3+
Step 2: Ce4+ + Mn3+ ---> Ce3+ + Mn4+
Step 3: Mn4+ + Tl+ ---> Tl3+ + Mn2+
(9) The proposed steps for a catalyzed reaction between Ce4+ and Tl+ are represented above. The
products of the overall catalyzed reaction are
(A) Ce4+ and Tl+
(B) Ce3+ and Tl3+ (C) Ce3+ and Mn3+
(D) Ce3+ and Mn4+
(E) Tl3+ and Mn2+
(10) The isomerization of cyclopropane to propylene is a first-order process with a half-life of 19 minutes
at 500 °C. The time it takes for the partial pressure of cyclopropane to decrease from 1.0 atmosphere to
0.125 atmosphere at 500 °C is closest to
(A) 38 minutes
(B) 57 minutes
(C) 76 minutes
(D) 152 minutes
(E) 190 minutes
(11) The graph above shows the results of a study of the reaction of X with a large excess of Y to yield Z.
The concentrations of X and Y were measured over a period of time. According to the results, which of the
following can be concluded about the rate of law for the reaction under the
conditions studied?
A) It is zero order in [X].
B) It is first order in [X].
C) It is second order in [X].
D) It is the first order in [Y].
E) The overall order of the reaction is 2.
12. What is the mole fraction of ethanol, C2H5OH, in an aqueous solution in which
the ethanol concentration is 4.6 molal?
(A) 0.0046
(B) 0.076
(C) 0.083
(D) 0.20
(E) 0.72
13. The weight of H2SO4 (molecular weight 98.1) in 50.0 milliliters of a 6.00-molar solution is
(A) 3.10 grams (B) 12.0 grams (C) 29.4 grams (D) 294 grams (E) 300. Grams
14. Which of the following has the lowest conductivity?
(A) 0.1 M CuS04
(B) 0.1 M KOH
(C) 0.1 M BaCl2
(D) 0.1 M HF
(E) 0.1 M HNO3
15. If 87 grams of K2 SO4 (molar mass 174 grams) is dissolved in enough water to make 250 milliliters of
solution, what are the concentrations of the potassium and the sulfate ions?
[K+]
[SO42¯]
(A) 0.020 M
0.020 M
(B) 1.0 M
2.0 M
(C) 2.0 M
1.0 M
(D) 2.0 M
2.0 M
(E) 4.0 M
2.0 M
16. One of the outermost electrons in a strontium atom in the ground state can be described by which of the
following sets of four quantum numbers?
(A) 5, 2, 0, ½
(B) 5, 1, 1, ½
(C) 5, 1, 0, ½
(D) 5, 0, 1, ½
(E) 5, 0, 0, 1/2
17. All of the following statements concerning the characteristics of the halogens are true EXCEPT: CH 7
ZUMDAHL
(A) The first ionization energies (potentials) decrease as the atomic numbers of the halogens increase.
(B) Fluorine is the best oxidizing agent.
(C) Fluorine atoms have the smallest radii.
(D) Iodine liberates free bromine from a solution of bromide ion.
(E) Fluorine is the most electronegative of the halogens.
18. The SbCl5 molecule has trigonal bipyramid structure. Therefore, the hybridization of Sb orbitals should be
(A) sp2
(B) sp3
(C) dsp2
(D) dsp3
(E) d2sp3
19. Of the following reaction, which involves the largest decrease in entropy?
(A) CaCO3(s) ---> CaO(s) + CO2(g)
(B) 2 CO(g) + O2(g) ---> 2 CO2
(C) Pb(NO3)3 + 2 KI ---> PbI2 + 2 KNO3
(D) C3H8 + O2 ---> 3 CO2 + 4 H2O
(E) 4 La + 3 O2 ---> 2 La2O3
20. If 87 grams of K2 SO4 (molar mass 174 grams) is dissolved in enough water to make 250 milliliters of
solution, what are the concentrations of the potassium and the sulfate ions?
[K+]
[SO42¯]
(A) 0.020 M
0.020 M
(B) 1.0 M
2.0 M
(C) 2.0 M
1.0 M
(D) 2.0 M
2.0 M
(E) 4.0 M
2.0 M
1.
2.
3.
13.
14.
A
A
C
C
D
4.
5.
6.
15.
16.
C
C
B
E
E
7.
8.
9.
17.
18.
D
B
B
D
D
10.
11.
12.
19.
20.
B
A
B
E
E
FREE RESPONSE
Question #2 A student is assigned the task of determining the mass percent of silver in an alloy of copper
and silver by dissolving a sample of the alloy in excess nitric acid and then precipitating the silver as AgCl.
First the student prepares 50. mL of 6 M HNO3 .
(a) The student is provided with a stock solution of 16 M HNO3 , two 100 mL graduated cylinders
that can be read to ±1 mL, a 100 mL beaker that can be read to ±10 mL, safety goggles, rubber
gloves, a glass stirring rod, a dropper, and distilled H2O.
(i) Calculate the volume, in mL, of 16 M HNO3 that the student should use for preparing 50. mL of
6 M HNO3 .
(ii) Briefly list the steps of an appropriate and safe procedure for preparing the 50. mL of 6 M HNO3.
Only materials selected from those provided to the student (listed above) may be used.
(iii) Explain why it is not necessary to use a volumetric flask (calibrated to 50.00 mL ±0.05 mL) to
perform the dilution.
(iv) During the preparation of the solution, the student accidentally spills about 1 mL of 16 M HNO3
on the bench top. The student finds three bottles containing liquids sitting near the spill: a bottle of
distilled water, a bottle of 5 percent NaHCO3(aq), and a bottle of saturated NaCl(aq). Which of the
liquids is best to use in cleaning up the spill? Justify your choice.
Then the student pours 25 mL of the 6 M HNO3 into a beaker and adds a 0.6489 g sample of the
alloy. After the sample completely reacts with the acid, some saturated NaCl(aq) is added to the
beaker, resulting in the formation of an AgCl precipitate. Additional NaCl(aq) is added until no more
precipitate is observed to form. The precipitate is filtered, washed, dried, and weighed to constant
mass in a filter crucible. The data are shown in the table below.
Mass of sample of copper-silver alloy
0.6489 g
Mass of dry filter crucible
28.7210 g
Mass of filter crucible and precipitate (1st weighing)
29.3587 g
Mass of filter crucible and precipitate (2nd weighing)
29.2599 g
Mass of filter crucible and precipitate (third weighing)
29.2598 g
(b) Calculate the number of moles of AgCl precipitate collected.
(c) Calculate the mass percent of silver in the alloy of copper and silver.
Question #4: “In part (i), coefficients should be in terms of lowest whole numbers. Assume that
solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the
substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by
the reaction.“
(a) Solid magnesium hydroxide is added to a solution of hydrobromic acid.
(i) Balanced equation:
ANSWER: Mg(OH)2 + 2 H+ → Mg2+ + 2 H2O
1 point is earned for the correct reactants.
2 points are earned for the correct products.
1 point is earned for correctly balancing the
equation for both mass and charge.
(ii) What volume, in mL, of 2.00 M hydrobromic acid is required to react completely with 0.10 mol
of solid magnesium hydroxide?
__________________________________________________________________________________________________________________
(b) Magnesium chlorate is heated gently.
(i) Balanced equation:
ANSWER: 2MgClO3  MgCl2 + 3O2
(ii) What element is reduced in this reaction? ________________________________________________
ANSWER: chlorine’s oxidation number changes from +4 to -1, therefore, it is reduced.
SCORING: 1 point is earned for identifying the correct element.
(c) A copper wire is dipped into a solution of silver(I) nitrate.
(i) Balanced equation:
ANSWER: Cu + 2 Ag+ → Cu2+ + 2 Ag
SCORING: 1 point is earned for the correct reactants.
2 points are earned for the correct products.
1 point is earned for correctly balancing the equation
for both mass and charge.
(ii) Describe what is observed as the reaction proceeds.
_____________________________________________________________________________________
_____________________________________________________________________________________
ANSWER: Silver metal will appear on the surface of the copper wire.
OR
The solution will turn blue.
OR
The copper wire will lose mass.
SCORING: 1 point is earned for any one of the observations.
Question #6: In an experiment, all the air in a rigid 2.0 L flask is pumped out. Then some liquid
ethanol is injected into the sealed flask, which is held at 35°C. The amount of liquid ethanol initially
decreases, but after five minutes the amount of liquid ethanol in the flask remains constant. Ethanol
has a boiling point of 78.5°C and an equilibrium vapor pressure of 100 torr at 35°C.
(a) When the amount of liquid ethanol in the flask is constant, is the pressure in the flask greater
than, less than, or equal to 100 torr? Justify your answer.
(b) The flask is then heated to 45°C, and the pressure in the flask increases. In terms of kinetic
molecular theory, provide TWO reasons that the pressure in the flask is greater at 45°C than 35°C.
In a second experiment, which is performed at a much higher temperature, a sample of ethanol gas
and a copper catalyst are placed in a rigid, empty 1.0 L flask. The temperature of the flask is held
constant, and the initial concentration of the ethanol gas is 0.0100 M. The ethanol begins to
decompose according to the chemical reaction represented below.
CH3CH2OH(g)  CH3CHO(g) + H2(g)
The concentration of ethanol gas over time is used to create the three graphs below.
(c) Given that the reaction order is zero, one, or two, use the information in the graphs to respond
to the following.
(i)Determine the order of the reaction with respect to ethanol. Justify your answer.
ANSWER: The order of the reaction is zero. The plot on the left is a straight line, indicating that the
rate of decrease in [ethanol] is constant as [ethanol] changes. Therefore the rate of reaction does
not depend on [ethanol]. 1 point is earned for the correct choice with a valid justification.
(ii) Write the rate law for the reaction.
ANSWER: rate = k
SCORING: 1 point is earned for writing the correct rate law
(iii) Determine the rate constant for the reaction, including units.
ANSWER: rate = k = [ethanol] (0.00200.0100) mol/L 2000 s t D D - = - _ = 4.0 × 10−6 M s−1
SCORING: 1 point is earned for the correct setup. 1 point is earned for the correct units
(d) The pressure in the flask at the beginning of the experiment is 0.40 atm. If the ethanol
completely decomposes, what is the final pressure in the flask?
ANSWER: The final pressure is 0.80 atm (twice the original pressure because the products
represent twice as many moles of gas as the reactant).
SCORING: 1 point is earned for the correct final pressure.
Question 2 (a) First the student prepares 50. mL of 6 M HNO3.
(i) Find the volume, mL, of 16 M HNO3 that the student should use to prepare 50. mL of 6 M HNO3.
SOLUTION:
moles before dilution = moles after dilution
MiVi= MfVf
(16 M)(Vi) = (6 M)(50. mL)
Vi= 19 mL or 20 mL (to one significant figure)
SCORING:
1 point is earned for the correct volume.
(ii) Briefly list the steps of an appropriate and safe procedure for preparing the 50. mL of 6 M
HNO3. Only materials selected from those provided to the student (listed above) may be used.
ANSWER: Wear safety goggles and rubber gloves. Then measure 19 mL of 16M HNO3 using a 100 mL
graduated cylinder. Measure 31 mL of distilled H2O using a 100 mL graduated cylinder. Transfer the
water to a 100 mL beaker. Add the acid to the water with stirring.
SCORING:1 point is earned for properly measuring the vol of 16M HNO3 & preparing 6 M HNO3 acid soln
1 point is earned for wearing protective gear and for adding acid to water.
(iii) Explain why it is not necessary to use a volumetric flask (calibrated to 50.00 mL ±0.05
mL) to perform the dilution.
ANSWER: The graduated cylinders provide sufficient precision in volume measurement to
provide two significant figures, making the use of the volumetric flask unnecessary.
SCORING: 1 point is earned for an acceptable explanation.
(iv) During the preparation of the solution, the student accidentally spills about 1 mL of 16 M HNO3
on the bench top. The student finds three bottles containing liquids sitting near the spill: a bottle of
distilled water, a bottle of 5 percent NaHCO3(aq), and a bottle of saturated NaCl(aq). Which of the
liquids is best to use in cleaning up the spill? Justify your choice.
ANSWER: NaHCO3(aq) should be used. The HCO3− ion will react as a base to neutralize the HNO3.
SCORING: 1 point is earned for the correct choice with explanation.