CHEM 1412 Practice Exam 1 - Chapters 12 – 14 Chang
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Some equations and constants:
T = Km
ln[A]t = –kt + ln[A]o
t1/2 = ln(2) / k
ln(k1/k2) = (Ea /R) (1/T2 – 1/T1)
P = XP°
 = MRT
1 / [A]t = kt + 1 / [A]o
t1/2 = 1 / k{A]o
Kp = Kc(RT)n
R = 0.08206 L atm mole–1 K–1 = 8.314 J mole–1 K–1
A periodic table is also attached to the end of the exam.
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For show work problems, you must show your calculations and units clearly for credit
or partial credit. Good luck!
1.
What is the molarity of a solution prepared by dissolving 10.0 g of KNO3 in 250 mL of solution?
2.
What is the molality of a solution made by dissolving 5.00 g of naphthalene, C10H8, in 50.0 mL of
ethanol? The density of ethanol is 0.790 g/mL.
3.
How many grams of NaCl are in 250 g of a 15.0% (by weight) solution?
4.
A solution of glucose, C6H12O6, has an osmotic pressure of 7.7 atm at 25°C. What is the molarity of this
solution?
5.
Aqueous concentrated nitric acid is 69% HNO3 by weight and has a density of 1.42 g/mL.
a) What is the molality of this solution?
b) What is the molarity of this solution?
6.
The vapor pressure of water at 25°C is 23.76 torr. What is the vapor pressure at 25°C of a
solution prepared by dissolving 0.300 mole of sucrose in 12.0 moles of water?
7.
What pressure of CO2 gas is required to keep a concentration of dissolved CO2 at 0.10 M in a can of soda?
The Henry’s law constant for CO2 dissolved in water is 0.034 M/atm at 25°C.
8.
A saturated solution
a) will dissolve additional solute if more solute is added.
b) contains no dissolved solute.
c) contains dissolved solute in equilibrium with undissolved solid.
d) will rapidly precipitate some solid solute if a seed crystal is added.
9.
Which one of the following substances will be the most soluble in water?
a) KBr
b) C10H8
c) CCl4
d) C8H18
10.
A 0.100 m solution of which one of the following solutes will have the highest boiling point?
a) KNO3
b) Ca(NO3)2
c) Al(NO3)3
d) Na2SO4
11.
The freezing point of a 1.0 M solution of NaCl in water is higher than the calculated value that assumes the
particle concentration for this solute is 2.0 M. This is due to
a) solvation of the ions
b) particle concentration greater than 2.0 M
c) hydrogen bonding
d) occurrence of ion pairing
12.
When NaCl dissolves in water,
a) the oxygens of the water molecules are attracted to the sodium ions.
b) the hydrogens of the water molecules are attracted to the chloride ions.
c) the sodium and chloride ions becomes separated due to solvation.
d) all of the above are true.
13.
What is the freezing point of a solution prepared by dissolving 15 g of KBr in 100 mL of water? The
freezing point depression constant, Kf, for water is 1.86 C/m.
14.
In the gas phase reaction below, if the rate of formation of NO2 is 8.24 X 10–4 M s–1, what is the rate of
disappearance of O2?
4 NH3 + 7 O2  4 NO2 + 6 H2O
15.
16.
Use the table of data shown below to calculate the value of the rate constant k. The reaction is first order.
time (s)
[A] (M)
0
10.0
20.0
30.0
40.0
0.124
0.102
0.0831
0.0681
0.0557
The reaction 2NO (g) + Br2 (g)  2NOBr (g) is second order with respect to NO and first order with
respect to Br2. Which is the correct rate law for this reaction?
a) Rate = k[NO][Br2]
c) Rate = k[NOBr]2
b) Rate = k[NO]2[Br2]
d) Rate = k[NO][Br2]2
17.
The correct units for the rate constant k in the rate law Rate = k[A]2[B] are
a) M s–1
b) M–1 s–1
c) M–2 s–1
d) M–1 s–2
18.
The rate law for the aqueous reaction H2SeO3 + 6 I– + 4 H+ –––> Se + 2 I3 + 3 H2O is
Rate = k[H2SeO3][I–]3[H+]2. By what factor will the rate increase if we double the concentrations of
all three reactants?
a) 8
b) 32
c) 64
d) 128
19.
Given the rate data below for the reaction 2A + 3B  Products, what is the rate law for this reaction?
–
Exp.
[A], M
[B], M
Rate, M sec–1
1
2
3
0.100
0.200
0.100
0.100
0.100
0.200
4.0 X 10–5
1.6 X 10–4
8.0 X 10–5
a) Rate = k[A][B]
20.
b) Rate = k[A]2[B]
c) Rate = k[A]2[B]2
d) Rate = k[A][B]2
When the concentration of a reactant was 0.100 M, the rate of the reaction was 8.42 X 10–6 M s-1.
When the concentration of the reactant was doubled to 0.200 M, the rate increased to 1.59 X 10–5 M s–1.
What is the order of the reaction with respect to this reactant (the value of “x” in the rate law) to three
significant figures?
21.
For a first order reaction, a plot of __________ vs. time gives a straight line with a slope of –k.
For a second order reaction, a plot of 1/[A]t vs. time gives a straight line with a slope of ________.
22.
The half-life of iodine-131, a radioactive isotope of iodine, is 8.04 days. If an iodine-131 solution is initially
0.100 M, what will the concentration be after 60 days? Radioactive decay is a first order process.
23.
A substance that forms in one step and is consumed in another step of a multistep reaction is
a) a transition state
b) an intermediate
c) a catalyst
d) a final product
24.
Which of the following will lower the activation energy for a reaction?
a) increasing the concentrations of reactants
b) raising the temperature of the reaction
c) adding a catalyst
d) increasing the total pressure
25.
The reaction NO2 + CO  NO + CO2 follows the rate law Rate = k[NO2]2.
In the mechanism below,
a) which step is the rate-limiting step?
__________
b) which substance is an intermediate in the reaction?
__________
Step 1
Step 2
26.
NO2 + NO2 –––> NO3 + NO
NO3 + CO –––> NO2 + CO2
In any multistep reaction mechanism, the rate of the overall reaction is determined by the rate of
the ________ step in the mechanism.
a) first
b) last
c) slowest
d) fastest
Answers
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
0.396 M
0.988 m
37.5 g
0.315 M
a) 35.3 m
b) 15.5 M
23.18 torr
2.94 atm
C
A
C
D
D
–4.7 °C
1.44 X 10–3 M/s
k = 0.0200 s–1
B
C
C
B
x = 0.917
ln[A]t, k
5.67 X 10–4 M
B
C
a) Step 1
b) NO3
C