Review for Chapters 5 & 6 Test
Objectives:
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Solve gas stoichiometry problems.
Calculate the molar mass (molecular weight) of a gas.
Calculate partial pressures of gases using Dalton’s Law.
Determine the molar volume of a gas.
Discuss kinetic molecular theory and how it is used to describe gases.
Describe how temperature, speed of particles, and kinetic energy of particles are all related.
Define effusion and diffusion.
Calculate the rate of effusion for gases.
Show how van der Waals equation accounts for real gases.
Explain when a real gas is close to an ideal gas.
Describe the energy flow between a system and its surroundings.
State the first law of thermodynamics.
Define exothermic and endothermic.
Define heat capacity.
Define enthalpy and calculate changes in enthalpy in a chemical reaction.
Show how a change in enthalpy is measured by calorimetry.
Show the relationship between q and H.
Calculate the change in enthalpy of a reaction using Hess’ Law.
Define standard states.
Use standard enthalpies of formation to calculate H for a reaction.
Additional practice problems to try from textbook:
Page 234: 57 (Gas Stoichiometry)
Page 282: 43 (Calorimetry)
Page 282: 34 (Enthalpy)
Page 283: 56 (Hess’s Law)
Page 284: 66 (Standard Enthalpies of Formation)
Also, review homework, weekly quizzes, pre-lab activity, lab calculations, etc.
Answers to problems listed above:
Chapter 5:
57(b) 13.3 L HCN
Chapter 6:
43. 0.25 J/gºC
34. (a) -286 kJ
(b) -572 kJ
(c) -3320 kJ
(d) -2.3 x 109 kJ
56. ΔH = -202.6 kJ
66. -4594 kJ
Chapter 5: Gases
1. The density of chlorine gas at STP, in grams per liter, is approximately:
(a) 6.2
(b) 3.2
(c) 3.9
(d) 4.5
(e) 1.3
2. What is the density of ammonia gas (NH3) at 2.00 atm pressure and a temperature of 25.0oC?
(a) 0.720 g/L
(b) 0.980 g/L
(c) 1.39 g/L
(d) 16.6 g/L
(e) 0.695 g/L
3. A container with volume 71.9 mL contains water vapor at a pressure of 10.4 atm and a
temperature of 465oC. How many grams of the gas are in the container?
(a) 0.421 g
(b) 0.183 g
(c) 0.129 g
(d) 0.363 g
(e) 0.222 g
4. What is the molecular weight of a pure gaseous compound having a density of 4.95 g/L at -35
o
C and 1020 torr?
(a) 24
(b) 11
(c) 72
(d) 120
(e) 44
5. Equal masses of three different ideal gases, X, Y, and Z, are mixed in a sealed rigid container.
If the temperature of the system remains constant, which of the following statements about the
partial pressure of gas X is correct?
(A) It is equal to 1/3 the total pressure
(B) It depends on the intermolecular forces of attraction between molecules of X, Y, and
Z.
(C) It depends on the relative molecular masses of X, Y, and Z.
(D) It depends on the average distance traveled between molecular collisions.
(E) It can be calculated with knowledge only of the volume of the container.
6. A mixture of 90.0 grams of CH4 and 10.0 grams of argon has a pressure of 250 torr under
conditions of constant temperature and volume. The partial pressure of CH4 in torr is:
(a) 143
(b) 100
(c) 10.7
(d) 239
(e) 26.6
7. What pressure (in atm) would be exerted by a mixture of 1.4 g of nitrogen gas and 4.8 g of
oxygen gas in a 200 mL container at 57oC?
(a) 4.7
(b) 34
(c) 47
(d) 27
(e) 0.030
8. A sample of hydrogen gas collected by displacement of water occupied 30.0 mL at 24oC on a
day when the barometric pressure was 736 torr. What volume would the hydrogen occupy if it
were dry and at STP? The vapor pressure of water at 24.0oC is 22.4 torr.
(a) 32.4 mL
(b) 21.6 mL
(c) 36.8 mL
(d) 25.9 mL
(e) 27.6 mL
9. Which one of the following statements is not consistent with the kinetic-molecular theory of
gases?
(a) Individual gas molecules are relatively far apart.
(b) The actual volume of the gas molecules themselves is very small compared to the
volume occupied by the gas at ordinary temperatures and pressures.
(c) The average kinetic energies of different gases are different at the same temperature.
(d) There is no net gain or loss of the total kinetic (translational) energy in collisions
between gas molecules.
(e) The theory explains most of the observed behavior of gases at ordinary temperatures
and pressures.
10. A mixture of 0.50 mol H2(g) and 0.50 mol N2(g) is introduced into a 15.0 liter container
having a pinhole leak at 30oC. After a period of time, which of the following is true?
(a) The partial pressure of H2 exceeds that of N2 in the container.
(b) The partial pressure of N2 exceeds that of H2 in the container.
(c) The partial pressures of the two gases remain equal.
(d) The partial pressures of both gases increase above their initial values.
(e) The partial pressure of H2 in the container increases above the initial value.
11. If helium effuses through a porous barrier at a rate of 4.0 moles per minute, at what rate (in
moles per minute) would oxygen gas diffuse?
(a) 0.20
(b) 0.50
(c) 2.0
(d) 8.0
(e) 1.41
12. A real gas most closely approaches the behavior of an ideal gas under conditions of:
(a) high P and low T
(b) low P and high T
(c) low P and T
(d) high P and T
(e) STP
13. Which one of the following statements about the following reaction is false?
CH4(g) + 2O2(g)
CO2(g) + 2H2O(g)
(a) Every methane molecule that reacts produces two water molecules.
(b) If 32.0 g of oxygen reacts with excess methane, the maximum amount of carbon
dioxide produced will be 22.0 g.
(c) If 11.2 liters of methane react with an excess of oxygen, the volume of carbon dioxide
produced at STP is (44/16)(11.2) liters.
(d) If 16.0 g of methane react with 64.0 g of oxygen, the combined masses of the
products will be 80.0 g.
(e) If 22.4 liters of methane at STP react with 64.0 g of oxygen, 22.4 liters of carbon
dioxide at STP can be produced.
14. What total gas volume (in liters) at 520oC and 880 torr would result from the decomposition
of 33 g of potassium bicarbonate according to the equation:
2KHCO3(s)
K2CO3(s) + CO2(g) + H2O(g)
(a) 56 L
(b) 37 L
(c) 10 L
(d) 19 L
(e) 12 L
15. Calculate the weight of KClO3 that would be required to produce 29.5 L of oxygen measured
at 127oC and 760 torr.
2KClO3(s)
2KCl(s) + 3O2(g)
(a) 7.82 g
(b) 12.2 g
(c) 14.6 g
(d) 24.4 g
(e) 73.5 g
16. Which of the following statements is false?
(a) The properties of N2(g) will deviate more from ideality at -100oC than at 100oC.
(b) Van der Waal's equation corrects for the non-ideality of real gases.
(c) Molecules of CH4(g) at high pressures and low temperatures have no attractive forces
between each other.
(d) Molecules of an ideal gas are assumed to have no significant volume.
(e) Real gases do not always obey the ideal gas laws.
17. The ideal gas law predicts that the molar volume (volume of one mole) of gas equals:
(a) gRT/PV
(b) (MW)P/RT
(c) 1/2ms-2
(d) RT/P
(e) 22.4 L at any temperature and pressure
18. Three 1.0 liter flasks are filled with H2, O2 and Ne, respectively, at STP.
Which of the following statements is true?
(a) Each flask has the same number of gas molecules.
(b) The velocity of the gas molecules is the same in each flask.
(c) The density of each gas is the same.
(d) There are twice as many O2 and H2 molecules as Ne atoms.
(e) None of the above is true.
19. Two flexible containers for a gas are at the same temperature and pressure. One holds 0.50
gram of hydrogen and the other holds 8.0 grams of oxygen. Which of the following statements
regarding these gas samples is FALSE?
(A) The volume of the hydrogen container is the same as the volume of the oxygen
container.
(B) The number of molecules in the hydrogen container is the same as the number of
molecules in the oxygen container.
(C) The density of the hydrogen sample is less than that of the oxygen sample.
(D) The average kinetic energy of the hydrogen molecules is the same as the average
kinetic energy of the oxygen molecules.
(E) The average speed of the hydrogen molecules is the same as the average speed of the
oxygen molecules.
20. A compound is heated to produce a gas whose molecular weight is to be determined. The gas
is collected by displacing water in a water-filled flask inverted in a trough of water. Which of the
following is necessary to calculate the molecular weight of the gas, but does NOT need to be
measured during the experiment?
(A) Mass of the compound used in the experiment
(B) Temperature of the water in the trough
(C) Vapor pressure of the water
(D) Barometric pressure
(E) Volume of water displaced from the flask
21. Equal numbers of moles of He(g), Ar(g), and Ne(g) are placed in a glass vessel at room
temperature. If the vessel has a pinhole-sized leak, which of the following will be true regarding
the relative values of the partial pressures of the Gas remaining in the vessel after some of the
gas mixture has effused?
A) PHe < PNe < PAr
B) PHe < PAr < PNe
C) PNe < PAr < PHe
D) PAr < PHe < PNe
E) PHe = PAr = PNe
Answers
1. (b) 2. (c) 3. (e) 4. (c) 5. (c) 6. (d) 7. (d) 8. (d) 9. (c) 10. (b) 11. (e) 12. (b)
13. (c) 14. (d) 15. (e) 16. (c) 17. (d) 18. (a) 19. (e) 20. (c) 21. (a)
Chapter 6: Thermochemistry
1. At a constant temperature, an ideal gas is compressed from 6.0 liters to 4.0 liters by a constant
external pressure of 5.0 atm. How much work is done on the gas?
(a) w = +10 liter atm
(b) w = -10 liter atm
(c) w = +30 liter atm
(d) w = -30 liter atm
(e) The answer cannot be calculated.
2. A system suffers an increase in internal energy of 80 J and at the same time has 50 J of work
done on it. What is the heat change of the system?
(a) +130 J
(b) +30 J
(c) -130 J
(d) -30 J
(e) 0 J
3. A coffee cup calorimeter having a heat capacity of 451 J/oC was used to measure the heat
evolved when 0.0300 mol of NaOH(s) was added to 1000 mL of 0.0300 M HNO3 initially at
23.000 oC. The temperature of the water rose to 23.639 oC. Calculate H (in kJ/mol NaNO3) for
this reaction. Assume the specific heat of the final solution is 4.18 J/goC; the density of each
solution is 1.00 g/mL; and the addition of solid does not appreciably affect the volume of the
solution.
HNO3(aq) + NaOH(s)
NaNO3(aq) + H2O(l)
(a) -63.7 kJ/mol
(b) -151 kJ/mol
(c) -2.55 kJ/mol
(d) -81.4 kJ/mol
(e) -98.6 kJ/mol
4. CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(l); H = - 889.1 kJ
Hf° H2O(l) = - 285.8 kJ / mole
Hf° CO2(g) = - 393.3 kJ / mole
What is the standard heat of formation of methane, Hf° CH4(g), as calculated from the
data above?
(A) -210.0 kJ/mole
(B) -107.5 kJ/mole
(C) -75.8 kJ/mole
(D) 75.8 kJ/mole
(E) 210.0 kJ/mole
5. Calculate the amount of work done for the conversion of 1.00 mole of Ni to Ni(CO)4 in the
reaction below, at 75oC. Assume that the gases are ideal. The value of R is 8.31 J/mol K.
Ni(s) + 4 CO (g)
Ni(CO)4(g)
(a) 1.80 x 103 J
(b) 8.68 x 103 J
(c) -1.80 x 103 J
(d) -8.68 x 103 J
(e) -494 J
6. All of the following have a standard heat of formation value of zero at 25oC and 1.0 atm
except:
(a) N2(g)
(b) Fe(s)
(c) Ne(g)
(d) H(g)
(e) Hg(l)
7. For which of the following reactions would the Ho for the reaction be labeled
(a) Al(s) + 3/2 H2(g) + 3/2 O2(g)
Al(OH)3(s)
(b) PCl3(g) + 1/2 O2(g)
POCl3(g)
(c) 1/2 N2O(g) + 1/4 O2(g)
NO(g)
(d) CaO(s) + SO2(g)
CaSO3(s)
(e) The Ho for all these reactions would be labeled Hfo.
8. Calculate
Ho for the reaction:
Na2O(s) + SO3(g)
Na2SO4(g) given the following information:
Ho
(1) Na(s) + H2O(l)
NaOH(s) + 1/2 H2(g)
(2) Na2SO4(s) + H2O(l)
(3) 2Na2O(s) + 2H2(g)
-146 kJ
2NaOH(s) + SO3(g) +418 kJ
4Na(s) + 2H2O(l)
+259 kJ
(a) +255 kJ
(b) -435 kJ
(c) -581 kJ
(d) +531 kJ
(e) -452 kJ
9. Calculate
Hfo?
Horxn for the following reaction at 25.0 oC:
Fe3O4(s) + CO(g)
3FeO(s) + CO2(g)
(kJ/mol) -1118
-110.5
-272
-393.5
(a) -263 kJ
(b) 54 kJ
(c) 19 kJ
(d) -50 kJ
(e) 109 kJ
10. Calculate the standard heat of formation, Hfo, for FeS2(s), given the following information:
2FeS2(s) + 5O2(g)
2FeO(s) + 4SO2(g)
Horxn = -1370 kJ
Hfo for SO2(g) = -297 kJ/mol Hfo for FeO(s) = -268 kJ/mol
(a) -177 kJ
(b) -1550 kJ
(c) -774 kJ
(d) -686 kJ
(e) +808 kJ
Hfo
11.
H2(g) + 1/2 O2(g)  H2O(l)
H° = x
2 Na(s) + 1/2 O2(g)  Na2O(s)
H° = y
Na(s) + 1/2 O2(g) + 1/2 H2(g)  NaOH(s)
H° = z
Based on the information above, what is the standard enthalpy change for the following reaction?
Na2O(s) + H2O(l) ---> 2 NaOH(s)
(A) x + y + z
(B) x + y - z
(C) x + y - 2z
(D) 2z - x - y
(E) z - x - y
12. C2H4(g) + 3 O2(g)  2 CO2(g) + 2 H2O(g) For the reaction of ethylene represented above,
H is - 1,323 kJ. What is the value of H if the combustion produced liquid water H2O (l), rather
than water vapor H2O(g)? (H for the phase change H2O(g)  H2O(l) is -44 kJ mol¯1.)
A) -1,235 kJ
B) -1,279 kJ
C) -1,323 kJ
D) -1,367 kJ
E) -1,411 kJ
13. How much heat is absorbed in the complete reaction of 3.00 grams of SiO2 with excess
carbon in the reaction below? Ho for the reaction is +624.7 kJ.
SiO2(s) + 3C(s)
SiC(s) + 2CO(g)
(a) 366 kJ
(b) 1.13 x 105 kJ
(c) 5.06 kJ
(d) 1.33 x 104 kJ
(e) 31.2 kJ
14. The standard heat of combustion of ethanol, C2H5OH, is 1372 kJ/mol ethanol. How much
heat (in kJ) would be liberated by completely burning a 20.0 g sample?
(a) 686 kJ
(b) 519 kJ
(c) 715 kJ
(d) 597 kJ
(e) 469 kJ
15. Which statement is incorrect?
(a) At constant pressure, H = E + P V
(b) The thermodynamic symbol for enthalpy is H.
(c) Change in enthalpy is a state function.
(d) For an endothermic process, H is negative.
(e) If the work done by the system is greater than the heat absorbed by the system, E is
negative.
Answers
1. (a) 2. (b) 3. (e) 4. (c)
14. (d) 15. (d)
5. (b) 6. (d) 7. (a) 8. (c) 9. (c) 10. (a) 11. (d) 12. (e) 13. (e)