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CHE 107 Fall 2019 Exam 2
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Question #: 1
What is the mole fraction NaCl in a salt solution that is 42% NaCl by mass? (Molar masses: NaCl = 58.44 g/mol; H2O = 18.02 g/mol) Mole fraction NaCl = 1 Report your answer with two significant figures. Do NOT include units in your answer. Do NOT use scientific notation.
1.
____________________________________________________________________________
Question #: 2
How many moles of sucrose (342 g/mol) must be added to 552 g of water (18.02 g/mol) to give a solution with 2.0 mm Hg less vapor pressure than pure water at 20 °C? The vapor pressure of pure water at 20 °C is 17.5 mm Hg.
A. 11.4 mol
B. 2.26 mol
C. 19.8 mol
D. 3.95 mol
____________________________________________________________________________
Question #: 3
What happens to each property as the concentration of dissolved sucrose (C12H22O11) increases? Fill in the blank with increases or decreases.
The boiling point of the solution 1 The freezing point of the solution 2
1.
2.
____________________________________________________________________________
Question #: 4
What is the osmotic pressure of a 0.0500 M MgSO4 solution at 25 °C?
A. 4.07 atm
B. 0.226 atm
C. 1.08 atm
D. 2.45 atm
____________________________________________________________________________
Question #: 5
What is the freezing point of an aqueous solution prepared by dissolving 3.0 moles of glucose (C6H12O6) into 2.0 kg of water? Kf for water is 1.86 °C/m.
A. –5.6 °C
B. –2.8 °C
C. –3.2 °C
D. –1.9 °C
____________________________________________________________________________
Question #: 6
Which solution will have the lowest boiling point?
A. 0.0020 m K3PO4
B. 0.0025 m Na2SO4
C. 0.0040 m KI
D. 0.0080 m C12H22O11
____________________________________________________________________________
Question #: 7
In a laboratory experiment, a student dissolves 1.02 grams of an unknown nonelectrolyte into 10.0 grams of benzene. The freezing point of the solution is –0.70 °C. The normal freezing point and freezing point depression constant of benzene is 5.50 °C and 5.12 °C/m, respectively. Use the data from the experiment to determine the molar mass of the unknown.
A. 84 g/mol
B. 97 g/mol
C. 71 g/mol
D. 8200 g/mol
____________________________________________________________________________
Question #: 8
Ammonia reacts with oxygen according to the equation 4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(g). If the rate ammonia consumption is 3.8 ×10–5 M/s, what is the rate of appearance of H2O(g)?
A. 1.9 ×10–5 M/s
B. 5.7 ×10–5 M/s
C. 4.6 ×10–5 M/s
D. 2.0 ×10–5 M/s
____________________________________________________________________________
Question #: 9
Use the table of experimental data to determine the orders of each reactant for the reaction: A(aq) + 3B(aq) → 2C(aq) + D(aq) .
Experiment [A] (M) [B] (M) Initial Rate (M/s)
1 0.080 0.034 2.2 × 10–4
2 0.080 0.017 1.1 ×10–4
3 0.16 0.017 2.2 ×10–4
The reaction is
A. 1st order in A, 3rd order in B
B. 1st order in A, 1st order in B
C. 2nd order in A, 1st order in B
D. 2nd order in A, 2nd order in B
____________________________________________________________________________
Question #: 10
Kinetic data was collected for the reaction 2 H2(g) + 2 NO(g) → 2 H2O(g) + N2(g) as shown below.
[H2] (M) [NO] (M) Initial Rate (M/s)
0.0100 0.0250 2.4 × 10–6
0.0050 0.0250 1.2 × 10–6 0.0100 0.0125 0.60 ×10–6
From this data, it was found that rate = k[H2][NO]2. What is the value of the rate constant, k? .
A. 0.16 M–2s–1
B. 0.38 M–2s–1
C. 1.4 × 10–4 M–2s–1
D. 0.011 M–2s–1
____________________________________________________________________________
Question #: 11
Label the graph of the second-order reaction below using the letter for the corresponding answers. Scroll down to see all of your answer choices and the blanks. Report each answer as one letter (A-J).
A time B 1/time
C [A]t
D [A]o
E ln[A]t
F ln[A]o
G 1/[A]t
H 1/[A]o
I –k
J k
x-axis 1 y-axis 2 y-intercept 3 slope 4
1.
2.
3.
4.
____________________________________________________________________________
Question #: 12
The reaction 2A → B is first order in A with a rate constant of 4.9 × 10–2 s–1. How long (in seconds) will it take for A to decrease from 0.88 M to 0.14 M? Time = 1 s Report your answer with two significant figures. Do NOT include units in your answer. Do NOT use scientific notation.
1.
____________________________________________________________________________
Question #: 13
The metal-catalyzed decomposition of N2O was studied to determine the overall order of the reaction. 2 N2O(g) →2 N2(g) + O2(g) As the reaction of N2O was monitored, half of the N2O reacted at 15 seconds, and all the remaining N2O reacted in the next 15 seconds. What is the order of the reaction?
A. zeroth-order
B. first-order
C. second-order
D. third-order
____________________________________________________________________________
Question #: 14
For the reaction A → 2B, the following data was collected. Starting with 0.40 M (time = 0 s), each measurement of time is observed when the concentration is one-half its previous amount.
[A] (M) time (s)
0.40 0
0.20 10
0.10 30
0.05 70
The rate law is either Rate = k, Rate = k[A] or Rate = k[A]2. Which is the rate law, and why?
A. Rate = k[A] because the coefficient of A in the balanced reaction is 1.
B. Rate = k[A] because the half-life is constant over the course of the reaction.
C. Rate = k[A]2 because the half-life increases over the course of the reaction.
D. Rate = k because the half-life is increasing over the course of the reaction.
____________________________________________________________________________
Question #: 15
Which action will increase the size of the rate constant, k?
A. increase temperature, T
B. increase the activation energy, Ea
C. decrease the frequency factor, A
D. decrease the pressure
____________________________________________________________________________
Question #: 16
The first-order rate constant for the reaction of methyl chloride (CH3Cl) with water to produce methanol (CH3OH) and hydrochloric acid (HCl) is 3.32 × 10–10 s–1at 25 °C. Calculate the rate constant at 55 °C if the activation energy is 116 kJ/mol.
A. 6.9 × 10–9 s–1
B. 2.4 × 10–8 s–1
C. 9.1 × 10–10 s–1
D. 3.4 × 10–12 s–1
____________________________________________________________________________
Question #: 17
Given the following elementary steps and overall reaction, which species is the reaction intermediate? Step 1: 2 NO2 → NO + NO3 Step 2: NO3 + CO → NO2 + CO2 Overall: NO2 + CO → NO + CO2
A. NO
B. NO2
C. NO3
D. CO
E. CO2
____________________________________________________________________________
Question #: 18
Examine the potential energy diagram for the reversible reaction: A + B ⇔ C + D.
The forward reaction is 1 [endothermic, exothermic] There are four arrows: blue arrow (1), purple arrow (2), orange arrow (3), and green arrow (4). Supply the number for the arrow that indicated the following energies: The activation energy for the forward reaction: 2 The activation energy for the reverse reaction: 3
1.
2.
3.
____________________________________________________________________________
Question #: 19
Given the following elementary steps and overall reaction, what is the rate law? Step 1 N2O → N2 + O slow Step 2 N2O + O → N2 + O2 fast Overall 2 N2O → 2 N2 + O2
.
A. rate = k[N2O]2
B. rate = k[N2O] C. rate = k[N2O]2[O]
D. rate = k[N2O][O]
____________________________________________________________________________
Question #: 20
A catalyst, when added to a reaction, 1 [increases, decreases] the rate of the reaction by 2 [increasing, decreasing] the magnitude of the activation energy. The catalyst 3 [is, is not] consumed in the overall reaction.
1.
2.
3.
____________________________________________________________________________
Question #: 21
Given I2(g) ⇔ 2 I(g) and Kc for this reaction is 3.8 × 10–5 at 727 °C, what can be said about the equilibrium reaction? .
A. The equilibrium favors products.
B. The equilibrium favors reactants.
C. The equilibrium favors neither reactants nor products.
D. No relationship between the amounts of reactants or products can be stated.
____________________________________________________________________________
Question #: 22
At 527 °C, a value of Kc for the decomposition of phosgene, COCl2, is given below. Supply the missing Kc values for the other two reaction equations.
Reaction Kc values
COCl2(g) ⇔ CO(g) + Cl2(g) 4.63 × 10–3
2 COCl2(g) ⇔ 2 CO(g) + 2Cl2(g) 1
CO(g) + Cl2(g) ⇔ COCl2(g) 2
Report your answer with three significant figures. Do NOT include units in your answer. For numbers in scientific notation, use the format 2.22E2 or 2.22E-2.
1.
2.
____________________________________________________________________________
Question #: 23
At 1000 K, pure NO2 gas decomposes: 2 NO2(g) ⇔ 2 NO(g) + O2(g) KP = 158.
If the initial partial pressures are PNO2 = 2.5 atm, PNO = 5.0, and PO2 = 0.50 atm, is the mixture at equilibrium? If not, which way will the reaction shift to achieve equilibrium?
A. Q >K; the reaction will shift to reactants.
B. Q <K; the reaction will shift to products.
C. Q >K; the reaction will shift to products.
D. Q <K; the reaction will shift to reactants.
E. Q = K; the reaction is at equilibrium and will not shift.
____________________________________________________________________________
Question #: 24
What is the value of Δn needed to convert between the given Kc and Kp for the following reaction? S(s) + O2(g) ⇔ SO2(g) Kc = 4.2 × 1052. Δn = 1 Enter your answer as an integer.
1.
____________________________________________________________________________
Question #: 25
Heating solid sodium bicarbonate in a closed vessel establishes the following equilibrium: 2 NaHCO3(s) ⇔ Na2CO3(s) + H2O(g) + CO2(g).
What would happen if • some CO2(g) were removed from the system? 1 [shift right, shift left, no shift] • some Na2CO3(s) were added to the system? 2 [shift right, shift left, no shift] • the volume of the container was reduced by 50%? 3 [shift right, shift left, no shift]
1.
2.
3.
____________________________________________________________________________
Question #: 26
Select the equilibrium constant expression (law of mass action), in terms of concentration, for the reaction: 2 I(g) ⇔ I2(s) .
A.
B.
C.
D.
____________________________________________________________________________
Question #: 27
Given the reaction CO2(g) + H2(g) ⇔ CO(g) + H2O(g) Kc = 0.52 at 686 °C, what is the concentration of CO(g), at equilibrium, given [H2] = 0.045 M, [CO2] = 0.086 M, and [H2O] = 0.040 M, all measured at equilibrium? .
A. 0.050 M
B. 0.075 M
C. 0.034 M
D. 0.025 M
____________________________________________________________________________
Question #: 28
Hydrogen and bromine react to form hydrobromic acid according to the reaction H2(g) + Br2(g) ⇔ 2 HBr(g) Kc = 2.18 × 106 at 730. °C. What is the equilibrium concentration of HBr if the initial concentrations of hydrogen and bromine are both 0.500 M?
A. 1.21 M
B. 0.262 M
C. 0.408 M
D. 0.999 M
____________________________________________________________________________
Question #: 29
Given N2(g) + O2(g) ⇔ 2 NO(g) and ΔG°= 173 kJ/mol at 298 K, what is ΔG when PN2 = PO2 = 5.5 atm and PNO = 32 atm at 298 K? .
A. 182 kJ/mol
B. 164 kJ/mol
C. 193 kJ/mol
D. 197 kJ/mol
____________________________________________________________________________
Question #: 30
At 25 °C, the ΔG° for the process H2O(l) ⇔ H2O(g) is 8.6 kJ/mol. Calculate the vapor pressure of water, in atm, at this temperature.
A. 0.97 atm
B. 1.1 ×10–14 atm
C. 0.099 atm
D. 0.031 atm
DRAFTDo Not Use Until Posted.
CHE 107 Fall 2019 Exam 2 - Confidential
Your Name: Your ID:
attachment_for_pubExamUID_lnxp115718547672446771XX_424.jpg
Question #: 1
What is the mole fraction NaCl in a salt solution that is 42% NaCl by mass? (Molar masses: NaCl
= 58.44 g/mol; H2O = 18.02 g/mol)
Mole fraction NaCl = 1
Report your answer with two significant figures. Do NOT include units in your answer. Do
NOT use scientific notation.
1. 0.18|.18|
Question #: 2
How many moles of sucrose (342 g/mol) must be added to 552 g of water (18.02 g/mol) to give a
solution with 2.0 mm Hg less vapor pressure than pure water at 20 °C? The vapor pressure of
pure water at 20 °C is 17.5 mm Hg.
A. 11.4 mol B. 2.26 mol C. 19.8 mol
✓D. 3.95 mol
Question #: 3
What happens to each property as the concentration of dissolved sucrose (C12
H22
O11
)
increases?
Fill in the blank with increases or decreases.
The boiling point of the solution 1
The freezing point of the solution 2
1. increases
2. decreases
Question #: 4
What is the osmotic pressure of a 0.0500 M MgSO4 solution at 25 °C?
.
A. 4.07 atm B. 0.226 atm C. 1.08 atm
✓D. 2.45 atm
Question #: 5
What is the freezing point of an aqueous solution prepared by dissolving 3.0 moles of glucose (C
6H12O6) into 2.0 kg of water?
Kf for water is 1.86 °C/m.
A. –5.6 °C
✓B. –2.8 °C C. –3.2 °C
D. –1.9 °C
Question #: 6
Which solution will have the lowest boiling point?
A. 0.0020 m K3PO4
✓B. 0.0025 m Na2SO4 C. 0.0040 m KI D. 0.0080 m C12H22O11
Question #: 7
In a laboratory experiment, a student dissolves 1.02 grams of an unknown nonelectrolyte into
10.0 grams of benzene.
The freezing point of the solution is –0.70 °C. The normal freezing point and freezing point
depression constant of benzene is 5.50 °C and 5.12 °C/m, respectively.
Use the data from the experiment to determine the molar mass of the unknown.
✓A. 84 g/mol
B. 97 g/mol C. 71 g/mol D. 8200 g/mol
Question #: 8
Ammonia reacts with oxygen according to the equation
4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(g).
If the rate ammonia consumption is 3.8 ×10–5 M/s, what is the rate of appearance of H2O(g)?
.
A. 1.9 ×10–5 M/s
✓B. 5.7 ×10–5 M/s C. 4.6 ×10–5 M/s D. 2.0 ×10–5 M/s
Question #: 9
Use the table of experimental data to determine the orders of each reactant for the reaction:
A(aq) + 3B(aq) → 2C(aq) + D(aq)
.
The reaction is
A. 1st order in A, 3rd order in B
✓B. 1st order in A, 1st order in B C. 2nd order in A, 1st order in B D. 2nd order in A, 2nd order in B
Question #: 10
Kinetic data was collected for the reaction 2 H2(g) + 2 NO(g) → 2 H2O(g) + N2(g) as shown
below.
From this data, it was found that rate = k[H2][NO]2. What is the value of the rate constant, k?
.
A. 0.16 M–2s–1
✓B. 0.38 M–2s–1
C. 1.4 × 10–4 M–2s–1
D. 0.011 M–2s–1
Question #: 11
Experiment [A] (M) [B] (M) Initial Rate (M/s)
1 0.080 0.034 2.2 × 10–4
2 0.080 0.017 1.1 ×10–4
3 0.16 0.017 2.2 ×10–4
[H2] (M) [NO] (M) Initial Rate (M/s)
0.0100 0.0250 2.4 × 10–6
0.0050 0.0250 1.2 × 10–6
0.0100 0.0125 0.60 ×10–6
Label the graph of the second-order reaction below using the letter for the corresponding
answers. Scroll down to see all of your answer choices and the blanks. Report each answer as
one letter (A-J).
x-axis 1
y-axis 2
y-intercept 3
slope 4
A time
B 1/time
C [A]tD [A]oE ln[A]tF ln[A]oG 1/[A]tH 1/[A]oI –k
J k
1. A
2. G
3. H
4. J
Question #: 12
The reaction 2A → B is first order in A with a rate constant of 4.9 × 10–2 s–1. How long (in
seconds) will it take for A to decrease from 0.88 M to 0.14 M?
Time = 1 s
Report your answer with two significant figures. Do NOT include units in your answer. Do
NOT use scientific notation.
1. 37|38|
Question #: 13
The metal-catalyzed decomposition of N2O was studied to determine the overall order of the
reaction.
2 N2O(g) →2 N2(g) + O2(g)
As the reaction of N2O was monitored, half of the N2O reacted at 15 seconds, and all the
remaining N2O reacted in the next 15 seconds. What is the order of the reaction?
.
✓A. zeroth-order
B. first-order C. second-order D. third-order
Question #: 14
For the reaction A → 2B, the following data was collected.
Starting with 0.40 M (time = 0 s), each measurement of time is observed when the concentration
is one-half its previous amount.
The rate law is either Rate = k, Rate = k[A] or Rate = k[A]2. Which is the rate law, and why?
A. Rate = k[A] because the coefficient of A in the balanced reaction is 1. B. Rate = k[A] because the half-life is constant over the course of the reaction.
✓C. Rate = k[A]2 because the half-life increases over the course of the reaction. D. Rate = k because the half-life is increasing over the course of the reaction.
Question #: 15
Which action will increase the size of the rate constant, k?
✓A. increase temperature, T
B. increase the activation energy, Ea C. decrease the frequency factor, A D. decrease the pressure
Question #: 16
The first-order rate constant for the reaction of methyl chloride (CH3Cl) with water to produce
methanol (CH3OH) and hydrochloric acid (HCl) is 3.32 × 10–10 s–1at 25 °C. Calculate the rate
constant at 55 °C if the activation energy is 116 kJ/mol.
A. 6.9 × 10–9 s–1
✓B. 2.4 × 10–8 s–1
C. 9.1 × 10–10 s–1
D. 3.4 × 10–12 s–1
Question #: 17
[A] (M) time (s)
0.40 0
0.20 10
0.10 30
0.05 70
Given the following elementary steps and overall reaction, which species is the reaction
intermediate?
.
A. NO B. NO2
✓C. NO3 D. CO E. CO2
Question #: 18
Examine the potential energy diagram for the reversible reaction: A + B ⇔ C + D.
The forward reaction is 1 [endothermic, exothermic]
There are four arrows: blue arrow (1), purple arrow (2), orange arrow (3), and green arrow (4).
Supply the number for the arrow that indicated the following energies:
Step 1: 2 NO2 NO + NO3Step 2: NO3 + CO NO2 + CO2Overall: NO2 + CO NO + CO2
The activation energy for the forward reaction: 2
The activation energy for the reverse reaction: 3
1. exothermic
2. 1
3. 2
Question #: 19
Given the following elementary steps and overall reaction, what is the rate law?
.
A. rate = k[N2O]2
✓B. rate = k[N
2O]
C. rate = k[N2O]2[O]
D. rate = k[N2O][O]
Question #: 20
A catalyst, when added to a reaction, 1 [increases, decreases] the rate of the reaction by
2 [increasing, decreasing] the magnitude of the activation energy. The catalyst 3 [is, is
not] consumed in the overall reaction.
1. increases|increase|increasing|
2. decreasing|decrease|decreases|
3. is not|isn't|not|
Question #: 21
Given I2(g) ⇔ 2 I(g) and Kc for this reaction is 3.8 × 10
–5 at 727 °C, what can be said about the
equilibrium reaction?
Step 1 N2O N2 + O slow
Step 2 N2O + O N2 + O2 fast
Overall 2 N2O 2 N2 + O2
.
A. The equilibrium favors products.
✓B. The equilibrium favors reactants. C. The equilibrium favors neither reactants nor products. D. No relationship between the amounts of reactants or products can be stated.
Question #: 22
At 527 °C, a value of Kc for the decomposition of phosgene, COCl2, is given below. Supply the
missing Kc values for the other two reaction equations.
Report your answer with three significant figures. Do NOT include units in your answer. For
numbers in scientific notation, use the format 2.22E2 or 2.22E-2.
1. 2.14E-5
2. 216|2.16E2|
Question #: 23
At 1000 K, pure NO2 gas decomposes:
2 NO2(g) ⇔ 2 NO(g) + O2
(g) KP
= 158.
If the initial partial pressures are PNO2 = 2.5 atm, PNO = 5.0, and PO2 = 0.50 atm, is the
mixture at equilibrium? If not, which way will the reaction shift to achieve equilibrium?
.
A. Q >K; the reaction will shift to reactants.
✓B. Q <K; the reaction will shift to products. C. Q >K; the reaction will shift to products. D. Q <K; the reaction will shift to reactants.
Reaction Kc values
COCl2(g) CO(g) + Cl2(g) 4.63 × 10–3
2 COCl2(g) 2 CO(g) + 2Cl2(g) 1
CO(g) + Cl2(g) COCl2(g) 2
•
•
•
E. Q = K; the reaction is at equilibrium and will not shift.
Question #: 24
What is the value of Δn needed to convert between the given Kc and Kp for the following
reaction?
S(s) + O2(g) ⇔ SO2(g) Kc = 4.2 × 1052.
Δn = 1
Enter your answer as an integer.
1. 0
Question #: 25
Heating solid sodium bicarbonate in a closed vessel establishes the following equilibrium:
2 NaHCO3(s) ⇔ Na2
CO3
(s) + H2
O(g) + CO2
(g).
What would happen if
some CO2(g) were removed from the system? 1 [shift right, shift left, no shift]
some Na2CO3(s) were added to the system? 2 [shift right, shift left, no shift]
the volume of the container was reduced by 50%? 3 [shift right, shift left, no shift]
1. shift right|right|
2. no shift|none|
3. shift left|left|
Question #: 26
Select the equilibrium constant expression (law of mass action), in terms of concentration, for
the reaction:
2 I(g) ⇔ I2(s)
.
A.
✓B.
C.
D.
Question #: 27
Given the reaction
CO2(g) + H2(g) ⇔ CO(g) + H2O(g) Kc = 0.52 at 686 °C,
what is the concentration of CO(g), at equilibrium, given [H2] = 0.045 M, [CO2] = 0.086 M, and
[H2O] = 0.040 M, all measured at equilibrium?
.
✓A. 0.050 M
B. 0.075 M C. 0.034 M D. 0.025 M
Question #: 28
Hydrogen and bromine react to form hydrobromic acid according to the reaction
H2(g) + Br2(g) ⇔ 2 HBr(g) Kc = 2.18 × 106 at 730. °C.
What is the equilibrium concentration of HBr if the initial concentrations of hydrogen and
bromine are both 0.500 M?
A. 1.21 M B. 0.262 M C. 0.408 M
✓D. 0.999 M
Question #: 29
Given N2(g) + O2(g) ⇔ 2 NO(g) and ΔG°= 173 kJ/mol at 298 K, what is ΔG when PN2 = PO2 =
5.5 atm and PNO = 32 atm at 298 K?
.
✓A. 182 kJ/mol
B. 164 kJ/mol C. 193 kJ/mol D. 197 kJ/mol
Question #: 30
At 25 °C, the ΔG° for the process H2
O(l) ⇔ H2
O(g) is 8.6 kJ/mol. Calculate the vapor pressure of
water, in atm, at this temperature.
A. 0.97 atm B. 1.1 ×10–14 atm C. 0.099 atm
✓D. 0.031 atm
