Download CHEMISTRY 102 Spring 2012 Hour Exam III Page 20 1. For the

CHEMISTRY 102
Hour Exam III
1.
Spring 2012
For the reaction 2 NCl3(g) ⇌ N2(g) + 3 Cl2(g), the equilibrium partial pressures are:
PNCl3 = 0.100 atm;
PN 2 = 2.30 atm;
PCl 2 = 0.0560 atm
Calculate Kp for this reaction.
a) 1.29
2.
b) 0.0404
c) 1.93
d) 0.273
e) 16.7
Consider the following exothermic reaction at equilibrium in a closed rigid container:
PCl3(g) + Cl2(g) ⇌ PCl5(g)
ΔH = 89 kJ
Which of the following statements is false?
a) Addition of PCl3 to the container will shift the equilibrium toward formation of more
PCl5.
b) An increase in temperature will shift the equilibrium toward formation of more PCl3.
c) A decrease in the volume of the container will shift the equilibrium toward formation
of more PCl5.
d) Addition of He(g) will have no effect on the equilibrium position.
e) Removal of PCl5 from the container will shift the equilibrium toward formation of
more PCl3.
3.
A 25.0 g piece of aluminum (which has a molar heat capacity of 24.03 J/C mol) is
heated to 82.4C and dropped into a coffee cup calorimeter containing water initially at
22.3C. The final temperature of the water and aluminum mixture is 24.9C. Calculate
the mass of water in the calorimeter. The specific heat capacity of water is 4.18 J/C g.
a) 120 g
4.
b) 6.6 g
c) 3200 g
d) 2100 g
e) 250 g
For which of the following processes is S expected to be positive?
a) I2(g)  I2(s)
b) H2O(l)  H2O(s)
c) CH3OH(g) + 3/2 O2(g)  CO2(g) + 2 H2O(l)
d) O2(g) + 2 CO(g)  2 CO2(g)
e) N2(g) at 2 atm  N2(g) at 1 atm (Assume constant T and n.)
Page 20
CHEMISTRY 102
Hour Exam III
5.
Which of the following always describes a process at equilibrium?
a) G = 1
6.
Spring 2012
b) H = TS
c) Q = 1
d) G = G
e) K = 1
Sulfur exists in two solid forms, rhombic and monoclinic. At 1 atmosphere the rhombic
form is stable at temperatures below 96C. Above 96C the monoclinic form is stable.
Which of the following statements (a-c) is/are true concerning the Smonoclinic  Srhombic
transition?
a) Rhombic sulfur has a more disordered structure than monoclinic sulfur.
b) Smonoclinic  Srhombic is an exothermic process.
c) The sign of G is negative for Smonoclinic  Srhombic at temperatures above 96C.
d) All of the statements (a-c) are true.
e) None of the statements (a-c) are true.
7.
Consider the following reaction and Kp value:
H2O2(g) ⇌ H2(g) + O2(g)
Kp = 2.0  105
If H2O2(g) at an initial pressure of 0.10 atm reacts in a rigid container, calculate the
equilibrium partial pressure of H2(g).
8.
a) 2.0  106 atm
b) 2.0  103 atm
d) 4.0  102 atm
e) 2.0  102 atm
c) 1.4  103 atm
Consider the following reaction at some temperature:
2 CO(g) + O2(g) ⇌ 2 CO2(g)
K = 4.0
Some CO and O2 are added to a 2.0 L container and the reaction proceeds to equilibrium.
At equilibrium, 6.0 mol of CO and 2.0 mol of O2 are present. At equilibrium, how many
mol of CO2 are present in the reaction container?
a) 2.0 mol
b) 4.0 mol
c) 6.0 mol
d) 12 mol
e) 24 mol
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CHEMISTRY 102
Hour Exam III
9.
Spring 2012
Consider the following standard enthalpies of formation:
for P4O10(s) = 2984 kJ/mol
for H2O(l) = 286 kJ/mol
for H3PO4(s) = 1279 kJ/mol
If 2.00 moles of H2O are reacted by the following reaction at constant pressure:
P4O10(s) + 6 H2O(l)  4 H3PO4(s)
which of the following statements is true?
a)
b)
c)
d)
e)
10.
139 kJ of heat will be released.
416 kJ of heat will be absorbed.
416 kJ of heat will be released.
832 kJ of heat will be absorbed.
832 kJ of heat will be released.
S for the vaporization of ethanol is 110. J/Kmol at its normal boiling point, 351 K.
C2H5OH(l)  C2H5OH(g)
S = 110. J/K
At 1 atm and 351 K, calculate H for this vaporization process.
a) 32.8 kJ
11.
b) 32.8 kJ
c) 110 J
d) 38.6 kJ
e) 38.6 kJ
S for the vaporization of ethanol is 110. J/Kmol at its normal boiling point, 351 K.
C2H5OH(l)  C2H5OH(g)
S = 110. J/K
At 1 atm and 351 K, calculate E for this vaporization process.
a) 32.8 kJ
12.
b) 35.7 kJ
c) 107 J
d) 2.92 kJ
e) 41.5 kJ
In the presence of ultraviolet light, the noble gas xenon (Xe) will react with fluorine (F2)
gas to produce solid XeF4. What is the correct expression of K for this reaction?
a) 1/[F2]2[Xe]
b) [XeF4]/[Xe][F2]2
d) 1/[F2]4[Xe]
e) 1/[F2][Xe]
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c) [XeF4]/[Xe][F2]4
CHEMISTRY 102
Hour Exam III
13.
Spring 2012
Three experiments were run at 273 K in order to study the equilibrium reaction:
N2(g) + 3 H2(g) ⇌ 2 NH3(g)
In each experiment, different amounts of gases were mixed together initially and were
then allowed to react to reach equilibrium. The table below summarizes the initial
concentrations of the gases for each experiment before any reaction took place.
Experiment
Initial
Concentrations
1
[N2] = 1.0 M
[H2] = 1.0 M
[NH3] = 0
2
[N2] = 0
[H2] = 0
[NH3] = 1.0 M
3
[N2] = 2.0 M
[H2] = 1.0 M
[NH3] = 3.0 M
After equilibrium is reached, which of the following statements (a-d) regarding these
experiments is true?
a) In experiment 1, the rate of the forward reaction at equilibrium will be greater than
the rate of the reverse reaction at equilibrium.
b) Equilibrium cannot be reached in experiment 2 because no reactants are present
initially.
c) After equilibrium is reached in each experiment, the calculated value of K should
be the same for all three experiments.
d) The calculated value of K should be larger for experiment 3 than for
experiment 2.
e) None of the above statements (a-d) are true.
14.
Consider the following generic reaction (which is assumed balanced) at some constant
temperature:
A(aq) + 2 B(aq) ⇌ C(aq)
K=?
2.00 moles of A and 3.00 moles of B are placed in a 6.00 L container, which then react
by the above reaction to reach equilibrium. At equilibrium, the concentration of A is
0.300 mol/L. What is the value of the equilibrium constant, K, for this reaction?
a) 1.3  103
15.
b) 0.025
c) 0.35
d) 0.59
e) 1.7
A spontaneous chemical reaction is favored by which of the following?
a)
b)
c)
d)
increasing enthalpy and increasing entropy
decreasing enthalpy and increasing entropy
increasing enthalpy and decreasing entropy
decreasing enthalpy and decreasing entropy
Page 23
CHEMISTRY 102
Hour Exam III
Spring 2012
Consider the following reaction and data for the next two questions:
2 SO2(g) + O2(g)  2 SO3(g)
ΔH of
Compound
396 kJ/mol
297 kJ/mol
?
SO3(g)
SO2(g)
O2(g)
16.
S
257 J/Kmol
248 J/Kmol
205 J/Kmol
Assuming H and S are temperature independent, at how many of the following four
temperatures will this reaction be spontaneous (assuming all gases are at 1 atm)?
T = 1000.C;
a) none
T = 500.C;
b) 1
T = 100.C;
c) 2
T = 25C
d) 3
d) 4 (The reaction will be spontaneous at all four of the temperatures.)
17.
At standard conditions, the reaction above is allowed to react to reach equilibrium.
If, at equilibrium, the partial pressures of O2(g) and SO3(g) are 0.50 atm and 2.0 atm
respectively, calculate the equilibrium partial pressure of SO2(g). Assume T = 25C.
a) 1.0  1012 atm
b) 0.60 atm
d) 1.0  1024 atm
e) 1.0  106 atm
c) 1.2 atm
-----------------------------18.
The reaction quotient for a system is 7.2  102. If the equilibrium constant for the system
is 36, what will happen as equilibrium is approached?
a)
b)
c)
d)
e)
19.
There will be a net gain in products.
There will be a net gain in reactants.
There will be a net gain in both products and reactants.
There will be no net gain in either products or reactants.
The equilibrium constant will decrease until it equals the reaction quotient.
Consider the terms internal energy, heat, work, and enthalpy. How many of these are
state functions?
a) 0 (none)
Page 24
b) 1
c) 2
d) 3
e) 4 (All are state functions.)
CHEMISTRY 102
Hour Exam III
20.
Spring 2012
Consider the following reaction at some temperature:
H2O(g) + Cl2O(g) ⇌ 2 HOCl(g)
K = 9.0
If 2.0 mol of H2O and 2.0 mol of Cl2O are placed in a 1.0 L container, what will be the
concentration of HOCl once equilibrium has been reached?
a) 0.30 M
21.
c) 0.90 M
d) 1.2 M
e) 2.4 M
Which of the following statements is true?
a)
b)
c)
d)
e)
22.
b) 0.60 M
The free energy, G, of the universe is constant.
The entropy, S, of the universe is constant.
The energy, E, of the universe is constant.
The amount of heat in the universe is constant.
The amount of work in the universe is constant.
Consider the following cyclic process carried out in two steps on a gas.
Step 1:
45 J of heat are added to the gas and 10 J of expansion work are
performed.
Step 2:
60 J of heat are removed from the gas as the gas is compressed back to the
initial state.
Which of the following statements (a-c) is/are true concerning this process?
a) For Step 1, the surroundings does work on the system.
b) For Step 2, E2 = 55 J.
c) For Step 2, w2 = 5 J.
d) All of these statements (a-c) are true.
e) None of these statements (a-c) are true.
23.
Calculate the bond energy for the NN single bond using the following data:
H of , N 2 H 4 (g ) = 95.4 kJ/mol N2H4
Bond energy of HH = 432 kJ/mol
Bond energy of NH = 391 kJ/mol
Bond energy of NN = 941 kJ/mol
a) 146 kJ/mol
b) 388 kJ/mol
Lewis structure of N2H4
c) 297 kJ/mol
d) 252 kJ/mol
e) 202 kJ/mol
Page 25
CHEMISTRY 102
Hour Exam III
24.
Spring 2012
Consider the reaction of ethene with F2:
C2H4(g) + 6 F2(g)
 2 CF4(g)
+ 4 HF(g)
H1 = ?
Assume the enthalpy change for the above reaction is H1. Using the following reactions
and their enthalpy changes, one can construct a thermochemical cycle to determine H1.
H2(g) + F2(g)  2 HF(g)
H2
C(s) + 2 F2(g)  CF4(g)
H3
2C(s) + 2 H2(g)  C2H4(g)
H4
Which of the following expressions for H1 is correct?
a) H1 = H4  H2  H3
b) H1 = 2 H2  2 H4 + H3
c) H1 = H3 + H2  2 H4
d) H1 = 6 H2 + 2 H3  H4
e) H1 = 2 H2  H4 + 2 H3
25.
100 mL of water is placed in a coffee cup calorimeter. When 1.0 g of a soluble ionic
solid is added, the temperature increases from 21.5C to 24.2C as the solid dissolves.
For the dissolving process, what are the correct signs for Ssys, Ssurr, and Suniv?
a)
b)
c)
d)
e)
26.
Ssys
Ssurr
Suniv

+
+
+


+

+



+
+
+
Which of the following statements is false?
a) The equilibrium position represents the lowest free energy state available to a
reaction.
b) Chemical reactions want to minimize free energy.
c) If the free energy of reactants is lower than the free energy of products, then the
forward reaction is spontaneous.
d) The value of the free energy change for a reaction is dependent on the temperature.
e) The equilibrium constant for a reaction at 25C is greater than one (K > 1) if G
(at 25C) is negative.
Page 26
CHEMISTRY 102
Hour Exam III
27.
For a certain process at 82C, G = 12.4 kJ and H = 9.2 kJ . Therefore, S for the
process is:
a) 9.0 J/K
28.
Spring 2012
b) 9.0 J/K
c) 39.0 J/K
d) 21.6 J/K
e) 21.6 J/K
Which of the following is true?
a) As long as the disorder of the surroundings is increasing, a process will be
spontaneous.
b) For any process, Ssurr and Ssys have opposite signs.
c) If Ssurr = Ssys , the process is at equilibrium.
d) A spontaneous endothermic reaction cannot have a negative Ssys value.
e) An exothermic reaction has a negative Ssurr value.
29.
For a particular reaction with H = 16.0 kJ, the equilibrium constant is 1.50  102 at
372C. Assuming H and S are temperature independent, calculate S for the
reaction.
a) 18.8 J/K
30.
b) 18.8 J/K
c) 10.0 J/K
d) 10.0 J/K
e) 25.0 J/K
Consider the reaction:
N2O4(g)  2 NO2(g)
where PNO2 = 0.29 atm and PN 2O4 = 1.6 atm. For this reaction at these conditions,
G = 1000 J and G = +6000 J. Which of the following statements about this reaction
is true?
a) The reverse reaction is spontaneous at these conditions.
b) At equilibrium, PN 2O4 will be greater than 1.6 atm ( PN 2O4 > 1.6 atm).
c) The value of K for this reaction is greater than 1 (K > 1).
d) The value for wmax (maximum work) for this reaction at these conditions is 6000 J
(wmax = 6000 J).
e) The reaction is endothermic.
31.
My answers for this Chemistry 102 exam should be graded with the answer sheet
associated with:
a) Form A
b) Form B
c) Form C
d) Form D
e) Form E
Solubility rules:
Page 27
CHEMISTRY 102
Hour Exam III
Spring 2012
SOLUBILITY RULES
1. Most nitrate salts are soluble.
2. Most salts of alkali metals and ammonium cations are soluble.
3. Most chloride, bromide, and iodide salts are soluble.
Exceptions: salts containing Ag+, Pb2+, and Hg22+ ions are insoluble.
4. Most sulfate salts are soluble.
Exceptions: sulfates containing Ca2+, Ba2+, Pb2+, and Hg22+ ions are insoluble.
5. Most hydroxide salts are insoluble.
Exceptions: hydroxides containing alkali metals, Ba2+, Sr2+, and Ca2+ ions are soluble.
6. Most sulfide, carbonate, chromate, and phosphate salts are insoluble.
Exceptions: salts of alkali metals and ammonium cations are soluble.
USEFUL CONSTANTS/EQUATIONS
K = °C + 273
ΔH = ΔE + Δ(PV)
PV = nRT
R = 0.08206 L atm/mol K
w = –PΔV = –RTΔn
(at constant P and T)
Avogadro's number, N = 6.022 × 1023
ΔSuniv = ΔSsurr + ΔSsys
1 atm = 760 torr = 760 mm Hg
ΔSuniv =
kinetic energy = (1/2) mv2
P1V1
PV
 2 2
n1T1
n 2 T2
; ΔSsurr =

ΔG° = –RT ln K
ΔG = ΔH – TΔS; ΔG° = ΔH° – TΔS°
Kp = K(RT)n
2
Sorxn   Soproducts   Soreactants
2
1 J = 1 kg m /sec
L  atm
R = 8.3145 J/molK = 0.08206
mol  K
ΔE = q + w
ΔG = ΔG° + RT ln Q;
101.3 J = 1 Latm
Page 28

ΔG = wmax
G orxn   Gf , products   Gf , reactants
Horxn   Hf , products   Hf , reactants
q = s  mass  T, s = specific heat capacity