Recommended Questions for Unit 7 Gases (chapter 5): ALL book questions are
recommended!!!! Here are a few samples:
1. What properties define a gas at a molecular level?
2. What effect will the following changes have on the volume of a fixed
amount of gas?
a. An increase in pressure at constant temperature
b. An increase in pressure coupled with an increase in temperature
3. What effect will the following changes have on the pressure of a fixed
amount of gas?
a. An increase in temperature at constant volume
b. An decrease in temperature coupled with a decrease in volume
4. Which of the following would not result in an increase in the volume of a
fixed gas?
a. An increase in temperature at constant pressure
b. A decrease in temperature at constant pressure
5. Containers A and B are at the same pressure and temperature, but the
volume of A is greater than that of B. Indicate whether a given gas would
have the same or different densities in the two containers. If the
densities are different, in which container is the density greater?
6. What is the pressure within a 10.0 L vessel containing 0.250 mol each of
oxygen, hydrogen, and carbon dioxide at 298 K?
7. What is the mole fraction of oxygen in the mixture containing 0.25 mol of
each oxygen, hydrogen, and carbon dioxide?
8. A comparison is made at STP of 0.50 mol H2(g) and 1.0 mol He(g).
Complete the statement: the two gases will a) have equal average
molecular kinetic energies, b) have equal average molecular speeds, c)
occupy equal volumes, d) have equal effusion rates.
9. A mixture of 5.0 x 10 -3 mol H2(g) and 5.0 x 10 -3 mol SO2(g) at 25oC is
introduced into a 10.0-L container having a “pinhole” leak. After a
period of time, the mole fraction of H2(g) in the remaining gas mixture
a) is the same as in the original mixture, b) is less than in the
original mixture, c) is greater than the original mixture, d) cannot be
determined relative to the original mixture
10. BE ABLE TO ANALYZE DIAGRAMS OF BAROMETERS, CLOSED-ENDED MANOMETERS,
AND OPEN-ENDED MANOMETERS both qualitatively and quantitatively
11. Calculate the height of a column of water (d = 1.00 g/mL) that exerts
the same pressure as a column of mercury (d = 13.6 g/mL) 760 mm high.
12. Without doing calculations, arrange the drawings in F5.5 so that the
pressures denoted in red are in increasing order
13. A helium-filled party balloon has a volume of 4.50 L at sea level,
where the atmospheric pressure is 748 Torr. Assuming the temperature
remains constant, what will be the volume of the balloon when it is taken
to a mountain resort at an altitude of 2500 m, where the atmospheric
pressure is 557 Torr?
14. A gas is enclosed in a cylinder fitted with a piston. The volume of
the gas is 2.00 L at 398 Torr. The piston is moved to increase the gas
pressure to 5.15 atm. Which of the following is a reasonable value for
the volume of the gas at the greater pressure? 0.20 L, 0.40 L, 1.00 L, or
16.0 L
15. A balloon indoors, where the temperature is 27oC, has a volume of 2.00
L. What will its volume be outdoors, where the temperature is -23oC if n
and P remain constant?
16. Calculate the volume occupied by 4.11 kg of methane gas, CH4, at STP.
17. Flask A contains oxygen gas at STP and Flask B contains oxygen gas at
100oC. What is the pressure at 100oC?
18. What is the pressure exerted by 0.508 mol oxygen in a 15.0 L container
at 303 K?
19. What is the volume occupied by 16.0G of ethane gas (C2H6) at 720 Torr
and 18oC?
20. If 0.550 g of a gas occupies 0.200 L at 0.968 atom and 289 K, what is
the molecular mass of the gas?
21. Calculate the molar mass of a liquid that, when vaporized at 100oC and
755 Torr, yields 185 mL of vapor that has a mass of 0.523 g.
22. Calculate the density of methane gas, CH4, in grams per liter at 25oC
and 0.978 atm.
23. Under what pressure must oxygen gas be maintained at 25oC to have a
density of 1.50 g/L?
24. How many liters of oxygen gas are consumed for every 10.0 L of carbon
dioxide gas produced in the combustion of liquid pentane (C5H12) if all
volumes are measured at STP?
25. In the chemical reaction used in automotive air-bag safety systems,
nitrogen gas is produced by the decomposition of sodium azide, NaN3, at a
somewhat elevated temperature. What volume of N2(g), measured at 25oC
and 0.980 atom, is produced by the decomposition of62.5 g of NaN3?
2NaN3(s)  2Na(l) + 3N2(g)
26. A 1.00 L sample of dry air at 25oC contains 0.0319 mol N2, 0.00856 mol
O2, 0.000381 mol Ar, and 0.00002 mol CO2. Calculate the partial pressure
of N2(g) in the mixture.
27. The main components of dry air, by volume, are 78.08% N2, 20.95% O2,
0.93% Ar, and 0.04% CO2. What is the partial pressure of each gas in a
sample of air at 1.000 atm?
28. Hydrogen produced in the following reaction is collected over water at
23oC when the barometric pressure is 742 Torr. What volume of the “wet”
gas will be collected in the reaction of 1.50 g Al(s) with excess HCl
(aq)? 2Al(s) + 6HCl(aq)  2AlCl3(aq) + 3H2(g)
29. Without doing detailed calculations, determine which of the following
is a likely value for urms of oxygen molecules at 0oC if urms of H2 at
0oC is 1838 m/s: 115 m/s; 460 m/s; 1838 m/s; 7352 m/s; 29,400 m/s
30. If compared under the same conditions, how much faster than helium
does hydrogen effuse through a tiny hole?
31. One percent of a measured amount of Ar(g) escapes through a tiny hole
in 77.3 s. One percent of the same amount of an unknown gas escapes
under the same conditions in 97.6 s. Calculate the molar mass of the
unknown gas.
32. Two cylinders of gas are used in welding. One cylinder is 1.2 m high
and 18 cm in diameter, containing oxygen gas at 2550 psi and 19oC. The
other is 0.76 m high and 28 cm in diameter, containing acetylene gas
(C2H2) at 320 psi and 19oC. Assuming complete combustion, which tank
will be emptied, leaving unreacted gas in the other?
33. How many liters of CO2(g) measured at 23oC and 779 Torr, are produced
when 4.45 x 10 7 kJ of heat evolved in the combustion of butane (C4H10)
if ∆H = -5.76 x 10 3 kJ
34. A gaseous hydrocarbon is found to be 11% hydrogen by mass
a. Find the empirical formula for the compound
b. Find the molar mass of the hydrocarbon if it has a density of 3.16
g/L at 1.43 atm and 25oC.
c. Find the molecular formula of the compound.
35. 100.8 g of O2 and 289.9 g of N2 are pumped into a 6.00 L SCUBA tank
that is kept at 20oC.
a. Find the partial pressure of each gas
b. Find the total pressure in the tank
36. A sample of NOCl(g) is placed in a sealed container. When equilibrium
is established PNO(g) is 0.458 atm. Find PCl2(g)
37. In a reaction that produces oxygen gas, 37.45 mL of gas was collected
over water at 25oC and 1.01 atom. The vapor pressure of water is 23.76
mm Hg at 25oC. How many moles of oxygen gas were collected?
38. The average velocity of a diatomic gaseous molecule is found to be 515
m/s at 25oC.
a. What is the molar mass of the molecule?
b. Identify the molecule.
39. Describe the volume and pressure adjustments that must be made in
order to use the ideal gas equation when a gas is at low temps and high
pressure? AP question may look like “explain why there are deviations in
the Ideal Gas Law under certain conditions”.
40. Calculate the pressure exerted by 12.23 mol carbon dioxide gas in a
5.21 L flask at 45.7 oC using the ideal gas and van der Waals equations
if a(CO2) = 3.59 L2atm/mol2 and b(CO2) = 0.0427 L/mol
41. Cylinder A contains 0.50 mol H2, is 1.00L, and at 35oC. Cylinder B
contains 0.50 mol Xe, is 0.50 L and at 35oC.
a. What is the ratio of pressures, H2:Xe, between the two cylinders.
Justify.
b. Is the average kinetic energy of the H2 molecules greater than,
equal to, or less than that of the Xe atoms? Justify.
c. How could the average kinetic energy of the molecules in either
cylinder be decreased? Explain.
d. Is the average speed of the H2 molecules greater than, equal to, or
less than that of the Xe atoms? Justify.
42. A metal container was filled with a gas at 120oC and sealed. Whatn
the gas cooled, the container imploded. Explain.
43. At very low temperatures, the actual partial pressure of C3H6 is less
than the value predicted using the ideal gas law. Explain.
44. When collecting gas over water, explain why the water levels inside
and outside the gas collection cylinder must be the same before the
volume of the gas is measured and recorded.