Extra Problems for Unit 4 (Honors & Regents) : Phases
of Matter and the Gas Laws
1. 100 mL of gas are enclosed in a cylinder under a pressure of 760. torr. What would the
volume of the same gas be at a pressure of 1520 torr?
2. A mass of gas is under a pressure of 760. mm Hg and occupies a volume of 525 mL. If
the pressure were doubled, what volume would the gas now occupy? Assume the
temperature remains constant.
3. A certain gas occupies a volume of 100. mL at a temperature of 20.0C. What will its
volume be at 10.0C, if the pressure remains constant?
4. A gas occupies a volume of 1.0 L at a temperature of 270C and 500. torr pressure.
Calculate the volume of the gas if the temperature is changed to 60.0C and the pressure to
700. torr.
5. Calculate the pressure required to compress 2.00 L of a gas at 700. mm Hg and 20.0C
into a container of 0.100 L capacity at a temperature of -150.0C.
6. 750. mL of gas at 300. torr pressure and 50.0C is heated until the volume of gas is
2000. mL at a pressure of 700. torr. What is the final temperature of the gas?
7. How many moles of gas are present in a 50. L steel cylinder if the pressure is 10. atm
and the temperature is 270C?
8. A mixture of nitrogen and oxygen gas is collected over water at 300C and 700 torr
pressure. If the partial pressure of nitrogen is 550 torr, what is the partial pressure of
oxygen?
9. If 40. L of nitrogen gas are collected over water at a pressure of .957 atm, what is the
volume of dry nitrogen at STP?
(The following problems are for HONORS ONLY)
10. The barometric pressure on the lunar surface is about 10-10 torr. At a temperature of
100. K, what volume of lunar atmosphere contains 106 molecules of gas?
11. Determine the molecular mass of a gas if 4.50 g of it occupies 4.0 L at 950. torr and
1820C.
12. Assuming ideal gas behavior, what is the molecular mass of a gas with a density of
2.50 g/L at 980C and 0.974 atm?
13. At 100.0C and 720 mm Hg, what is the density of carbon dioxide, CO2?
14. The density of a gas is measured as 0.222 g/L at 20.00C and 800. torr. What volume
will 10.0 g of this gas occupy under standard conditions?
15. If CO2 diffuses from a flask in 30 seconds and an unknown gas diffuses from the
same flask in 2 minutes, calculate the molar mass of the unknown gas.
16. 45 seconds are required for a given number of moles of hydrogen to effuse through a
small opening. How long will it take for the same number of moles of oxygen to escape if
the starting conditions are the same?
17. Given the balanced equation
4NH3 (g) + 5 O2 (g) ----> 4NO(g) + 6H2O(g)
How many grams of NH3 will be required to react with 2.50 L of O2 at 25oC and 752
torr?
18. A chemist performs the following reaction
2KClO3(s) ---> 2KCl(s) + 3 O2(g)
She collects the O2 gas by water displacement at 20.0C. She observes a pressure of 753
mm Hg. Assuming the pressure of water vapor is 17.5 mm Hg at 200C and she started
with 1.28 g of potassium chlorate, what volume of gas is produced?
Answers: (1) 50.0 mL ; (2) 263 mL ; (3) 96.6 mL ; (4) 0.79 mL ; (5) 5880 mm Hg ; (6)
17400C ; (7) 20 moles ; (8) 118 torr ; (9) 34 L ; (10) 1.04 x 10-4 L ; (11) 34.7 g/mol ;
(12) 78.1 g/mol ; (13) 1.32 g/L ; (14) 44.2 L ; (15) 704 g/mol ; (16) 180 s ; (17) 1.37 g ;
(18) 0.388 L
The following is an example of an Honors test for Unit 4:
1. At constant temperature, which line shows the relationship between the volume of an
ideal gas and its pressure? (Diagram is available from Ms. Fed)
a) A b) B c) C d) D
2. Solid substances are most likely to sublime if they have
a) high vapor pressures and weak intermolecular attractions b) high vapor pressures and
strong intermolecular attractions
c) low vapor pressures and strong intermolecular attractions d) low vapor pressures and
weak intermolecular attractions
3. One reason that a real gas deviates from an ideal gas is that the molecules of the real
gas have
a) forces of attraction for each other b) a negligible volume c) no net loss of energy on
collision d) a straight line motion
4. Theoretically the volume of an IDEAL gas at absolute zero is
a) 100 mL b) 10 mL c) 0 mL d) 1000 mL
5. The normal freezing point of water is
a) 373 K b) 0 K c) 273 K d) 32oC
6. Convert 0.451 atm to torr
a) 248 torr b) 553 torr c) 0.683 torr d) 343 torr e) 395 torr
7. When the temperature remains constant, what is the new volume of a quantity of gas
which had a volume of 27.1 L at 2.18 atm when the pressure is increased to 10.1 atm?
a) 5.85 L b) 126 L c) 7.67 L d) 23.6 L e) 10.3 L
8. If the temperature of an ideal gas is raised from 150oC to 300oC, while the pressure
remains constant, the volume
a) doubles b) remains the same c) goes to 1/2 the original volume d) none of these
9. Calculate the volume occupied by a gas at 35oC if it occupies 285 mL at 100oC.
Assume constant pressure.
a) 470 mL b) 235 mL c) 879 mL d) 445 mL
10. Two moles of gas A spontaneously convert to three moles of gas B in a container
where the temperature and pressure are held constant. The sample originally took up 10.2
L of volume. What is the new volume of the products?
a) 0.189 L b) 6.73 L c) 12.3 L d) 1.15 L e) 15.3 L
11. If the temperature and pressure are held constant, the volume and number of moles of
a gas are
a) independent of each other b) equal c) directly proportional d) inversely proportional
12. Which of the following statements is true of 35.5 g of chlorine gas at STP?
a) it contains 6.02 x 1023 molecules b) it contains the same number of molecules as 1/2
mol of oxygen gas at STP
c) it occupies a volume of 22.4 L d) it exists in the form of ions
13. A mole of a gas at STP has a volume of 22.4 L. If the volume increases to 29.1 L and
the pressure is changed to 813 torr, calculate the new temperature.
a) 461 K b) 792 K c) 379 K d) 519 K e) 226 K
14. A 4.0 g piece of solid CO2 (dry ice) is allowed to vaporize. The final volume of the
balloon is 1.00 L at 300. K. What is the pressure of the gas?
a) 2.46 atm b) 246 atm c) 0.122 atm d) 122 atm e) none of these
15. For questions 15 & 16:
Zinc metal is added to hydrochloric acid to generate hydrogen gas, which is collected
over water at 20.0oC. (v.p. of water is 18 torr). The volume of the mixture is 1.7 L, and its
total pressure is 0.810 atm.
15. Determine the partial pressure of the hydrogen gas in this mixture
a) 562 torr b) 580 torr c) 598 torr d) 616 torr e) 634 torr
16. Determine the number of moles of hydrogen gas present in the sample
a) 42 mol b) 0.82 mol c) 1.3 mol d) 0.056 mol e) 22 mol
17. What would happen to the average kinetic energy of the molecules of a gas sample if
the temperature of the sample decreased from 40.oC to 20.oC?
a) it would become half its value b) it would double c) it would increase d) it would
decrease
18. Which of the following is not a property of gases?
a) they have low densities b) they are easily compressed c) they have definite shape d)
they fill the entire volume of their container e) all of the above are properties of gases
19. Ammonium nitrite undergoes decomposition to produce only gases as shown:
NH4NO2(s) -----> N2(g) + 2H2O(g)
How many liters of gas will be produced by the decomposition of 35.0 g of ammonium
nitrite at STP?
a) 12.3 L b) 24.5 L c) 36.8 L d) 29.5 L
20. Arrange the following gases in order of increasing molecular speed at 25oC.
Cl2, O2, F2, N2
a) Cl2, F2, O2, N2 b) Cl2, O2, F2, N2 c) N2, F2, Cl2, O2 d) Cl2, F2, N2, O2
21. Under which conditions does a real gas deviate most from ideal behavior?
a) at high temperatures and low pressures b) at high temperatures and high pressures c) at
low temperatures and low pressures d) at low temperatures and high pressures
22. Which sample of water has the least vapor pressure?
a) 40 mL at 35oC b) 20 mL at 30oC c) 200 mL at 25oC d) 100 mL at 20oC
23. The density of a gas is 3.00 g/L at STP. What is the molar mass of the gas?
a) 7.47 g/mol b) 22.4 g/mol c) 67.2 g/mol d) 11.2 g/mol
24. Which substance readily sublimes at room temperature?
a) C(s) b) H2O (l) c) I2(s) d) O2(g)
25. At 298 K, the vapor pressure of C2H5OH is greater than the vapor pressure of H2O.
The best explanation for this is that C2H5OH has
a) smaller molecules b) a smaller molecular mass c) weaker ionic bonds d) weaker
intermolecular forces
26. A large flask is evacuated and found to weigh 134.567 g. It is then filled to a pressure
of 735 mm Hg at 31oC with a gas of unknown molecular mass and then reweighed: its
mass is 137.456 g. The flask is then filled with water and again weighed: its mass is now
1067.9 g. Assuming that the ideal gas equation applies, what is the molar mass of the
unknown gas? (The density of water at 31oC is 0.997 g/mL)
27. Refer to the following figure, (obtainable from Ms. Fed), and describe all the phase
changes that would occur in each of the following cases. (a) water vapor originally at 1.0
x 10-3 atm and -0.10oC is slowly compressed at constant temperature until the final
pressure is 10 atm . (b) water originally at -10oC and 0.30 atm is heated at constant
pressure until the temperature is 80.0oC.
28. O2 gas effuses through a pin hole in 5.0 seconds. How long will it take an equivalent
amount of CO2 gas to effuse under the same conditions?
29. Carbon dioxide gas is collected over water by the addition of aqueous hydrochloric
acid to calcium carbonate.
CaCO3(s) + 2HCl(aq) -----> CaCl2(aq) + H2O(l) + CO2(g)
What volume of dry carbon dioxide would be collected ar 774 torr total pressure and
60.oC after the complete reaction of 10.0 g of CaCO3 with acid?
Answers: 1 b, 2 a, 3 a, 4 c, 5 c, 6 d, 7 a, 8 d, 9 b, 10 e, 11 c, 12 b, 13 c, 14 e,
15 c, 16 d, 17 d, 18 c, 19 c, 20 a, 21 d, 22 d, 23 c, 24 c, 25 d, 26) 79.7 g/mol,
27. a) vapor ---> solid (b) solid ---> water ---> vapor, 28) 5.9 seconds 29)
3.32 L