General Chemistry II - CHM202 Midterm Examination – Sample

General Chemistry II - CHM202
Midterm Examination – Sample
1. 2.50 mol NOCl was placed in a 2.50 L reaction vessel at 400ºC. After equilibrium was
established, it was found that 28% of the NOCl had dissociated according to the equation
2NOCl(g) →2NO(g) + Cl2(g).
Calculate the equilibrium constant, Kc, for the reaction.
A) 0.039
B) 26
C) 0.021
D) 47
E) 0.169
2. The molar heats of sublimation and fusion of iodine are 62.3 kJ/mol and15.3 kJ/mol,
respectively. Calculate the molar heat of vaporization of liquid iodine.
A) 4.07 kJ/mol
B) –47.0 kJ/mol
C) 77.6 kJ/mol
D) 47.0 kJ/mol
E) –77.6 kJ/mol
3. 1.25 moles of NOCl were placed in a 2.50 L reaction chamber at 427ºC. After equilibrium was
reached, 1.10 moles of NOCl remained. Calculate the equilibrium constant, Kc, for the reaction
2NOCl(g) → 2NO(g) + Cl2(g).
A) 4.1 x 10–3
B) 3.0 x 10–4
C) 5.6 x 10–4
D) 1.8 x 103
E) 1.4 x 10–3
4. Given the following liquids and their boiling points, which has the highest vapor pressure at its
normal boiling point?
A) methanol, bp = 65°C
B) water, bp = 100°C
C) benzene, bp = 80°C
D) The vapor pressure of each of the liquids at its normal boiling point would be the same.
E) ethanol, bp = 78°C
5. What is the slope of an Arrhenius plot for the following reaction?
2NOCl → 2NO + Cl2
Temperature (K)
k (L/mol·s)
400.
6.6 x 10–4
500.
2.9 x 10–1
600.
16.3
A) not enough information to calculate the slope
B) –1.22 x 104 K
C) –1.96 x 104 K
D) 8.18 x 10–2 K
E) 5.06 x 10–2 K
6. Consider this gas phase equilibrium system:
PCl5(g) → PCl3(g) + Cl2(g) ΔHºrxn = +87.8 kJ/mol.
Which of these statements is false?
A) A catalyst speeds up the approach to equilibrium and shifts the position of equilibrium to
the right.
B) Decreasing the total pressure of the system shifts the equilibrium to the right.
C) Increasing the temperature shifts the equilibrium to the right.
D) Increasing the temperature causes the equilibrium constant to increase.
E) Increasing the system volume shifts the equilibrium to the right.
7. It takes 42.0 min for the concentration of a reactant in a first-order reaction to drop from 0.45 M
to 0.32 M at 25°C. How long will it take for the reaction to be 90% complete?
A) 222 min
B) 137 min
C) 13.0 min
D) 284 min
E) 86.0 min
8. For which of the following species are the dispersion forces strongest?
A) C5H12
B) C7H16
C) C4H10
D) C8H18
E) C6H14
9. The molar enthalpy of vaporization of boron tribromide is 30.5 kJ/mol, and its normal boiling
point is 91°C. What is the vapor pressure of BBr3 at 20°C?
A) 311 torr
B) 5.31 torr
C) 143 torr
D) 66.1 torr
E) 11.5 torr
10. Which of these situations will result if some CH4(g) is removed from the reaction
CO(g) + 3H2(g) → CH4(g) + H2O(g) at equilibrium?
A) Kp will decrease.
B) No change will occur.
C) More CH4 and H2O will be produced.
D) H2O will be consumed.
E) More CO will be produced.
11. Sodium carbonate, Na2CO3(s), can be prepared by heating sodium bicarbonate, NaHCO3(s).
2NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g) Kp = 0.23 at 100ºC
If a sample of NaHCO3 is placed in an evacuated flask and allowed to achieve equilibrium at
100ºC, what will the total gas pressure be?
A) 0.23 atm
B) 0.11 atm
C) 0.48 atm
D) 0.96 atm
E) 0.46 atm
12. A certain reaction A → products is second order in A. If this reaction is 85% complete in 12
minutes, how long would it take for the reaction to be 15% complete?
A) 22 s
B) 110 s
C) 27 s
D) 62 s
E) 130 s
13. Chlorine dioxide reacts in basic water to form chlorite and chlorate according to the following
chemical equation:
2ClO2(aq) + 2OH–(aq) → ClO2–(aq) + ClO3–(aq) + H2O(l)
A kinetic study of this reaction under a certain set of conditions yielded the data below.
Exp [ClO2] (M)
[OH–] (M)
-Δ[ClO2] /Δt (M/s)
1
0.0500
0.100
5.75 x 10–2
2
0.100
0.100
2.30 x 10–1
3
0.100
0.0500
1.15 x 10–1
Which one of the following is the rate law for this reaction?
A) rate = k[ClO2]4[OH-]
B) rate = k[ClO2]2[OH-]2
C) rate = k[ClO2]2[OH-]
D) rate = k[ClO2][OH-]
E) rate = k[ClO2][OH-]2
14. In how many grams of water should 25.31 g of potassium nitrate (KNO3) be dissolved to
prepare a 0.1982 m solution?
A) 7,917 g
B) 250.0 g
C) 1,263 g
D) 792.0 g
E) 1,000. g
15. Which one of the following substances crystallizes as a molecular solid?
A) CH3OH
B) Al2(SO4)3
C) KI
D) SiO2
E) Sn
16. Based on the phase diagram shown below, how will the melting point of the substance change if
the pressure is increased above 1 atm?
A)
B)
C)
D)
The substance will not melt at pressures of 1 atm and above; instead, the solid sublimes to
form the gas phase.
The melting point will decrease.
The melting point will remain the same.
The melting point will increase.
17. Use the graph of vapor pressure to determine the normal boiling point of O2.
A)
B)
C)
D)
E)
84 K
92 K
90 K
O2 doesn't boil because it is always a gas.
88 K
18. For the reaction C6H14(g) → C6H6(g) + 4H2(g), ΔP(H2)/Δt was found to be 2.5 x 10–2 atm/s,
where ΔP(H2) is the change in pressure of hydrogen. Determine ΔP(C6H14)/Δt for this reaction at
the same time.
A) –2.5 x 10–2 atm/s
B) 2.5 x 10–2 atm/s
C) 0.10 atm/s
D) 6.2 x 10–3 atm/s
E) –6.2 x 10–3 atm/s
19. The solubility of CO2 gas in water
A) decreases with increasing temperature.
B) is not dependent on temperature.
C) decreases with decreasing temperature.
D) increases with increasing temperature.
20. Oxygen gas makes up 21% of the atmosphere by volume. What is the solubility of O2(g) in
water at 25°C if the atmospheric pressure is 741 mmHg? The Henry's law constant for oxygen
gas at 25°C is 1.3 x 10–3 mol/L·atm.
A) 0.96 M
B) 9.6 x 10–3 M
C) 2.7 x 10–4 M
D) 6.2 x 10–3 M
E) 1.3 x 10–3 M
21. Use the following data to determine the molar heat of vaporization of chlorine.
T (°C)
–84.5
–71.2 –47.3
P (mmHg)
40.0
100.0 400.0
A) 712 J
B) 34,700 J
C) 21,900 J
D) 9.99 kJ
E) 317 J
22. Which of the following substances should have the lowest boiling point?
A) CBrF3
B) CBr4
C) CBr3F
D) CF4
E) CBr2F2
23. At 10°C one volume of water dissolves 3.10 volumes of chlorine gas at 1.00 atm pressure. What
is the Henry's Law constant in mol/L·atm?
A) 36.
B) 3.1
C) 0.043
D) 0.13
E) 3.8
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