Gases Problems and Questions
Answer questions with complete sentences, including an indication of the question that was asked. Justify answers as
necessary. Show all work on problems including the equation used. Circle your answer including units and significant
figures. Use the GUESS method to solve problems.
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What is kinetic theory?
When kinetic theory is applied to gases, what assumptions are made about the particles in the gases?
How is temperature related to KE?
Suppose that a glass of warm water has a temperature of 45oC. Do all of the water molecules in the glass have
the same KE?
Is 10oC really twice at warm as 5oC? Explain, considering kinetic energy. Hint: think about absolute
temperature.
What temperature is “absolute zero” and what would be true about the particles in a substance at this
temperature?
Room temperature is usually about 22oC. What temperature is this on the Kelvin scale?
The coldest temperature ever recorded in Polson equals 249 K. What temperature is this on the Celsius scale?
You can walk across snow in snowshoes, but you sink if you try walking in regular shoes or boots. Using the
equation for pressure in your answer, explain why this is so.
What does a barometer measure?
On top of Mt. Everest, a typical air pressure measurement would be 33.7 kPa. What would this measurement
equal in millimeters of Mercury (mm Hg)?
The maximum air pressure recommended for a set of tires is 38 psi. What is the pressure in atmospheres (atm)?
What is this pressure in kPa?
Answers: (7) 295 K, (8) -24oC, (11) 253 mmHg, (12) 2.6 atm, 260 kPa
ALTERNATIVE ASSIGNMENT: Instead of completing problem #13-40, write two of your own problems for each of the
seven gas law equations that were covered in class. Calculate the answer to each of your problems. Also, write two of
your own gas stoichiometry problems (like #35-40)—be sure to include the balanced chemical equation in your
problems and calculate the answers to each. There should be 16 of your own problems (in addition to #1-12).
Boyle’s Law (constant T): P ·V = k or P1·V1 = P2·V2
P-T Law (constant V): P / T = k or P1 / T1 = P2 / T2
Charles’s Law (constant P): V / T = k or V1 / T1 = V2 / T2
13. Why does decreasing the temperature of a gas in a container decrease the pressure? Refer to the equation for
pressure when answering this question (P = F/A).
14. How are the variables proportional in Boyle’s law, Charles’ law, and the P-T law?
15. When driving a car on a hot day, it is common for the tires to increase in pressure. Why does this happen and
which gas law applies?
16. When a gas at constant temperature is compressed to a smaller volume, what happens to the pressure and
why?
17. What happens to a balloon if it is placed into a freezer and why?
18. If a gas is at STP (standard temperature and pressure), what is the temperature (in K) and the pressure (kPa)?
19. At constant temperature, 4.5 L of air at 92.6 kPa is compressed to 1.9 L. What is the new pressure? What law
was used?
20. A 3.8 L balloon at 24oC is placed into a freezer at -12oC. What is the new volume if the pressure remains the
same? What law was used?
21. A fixed volume of gas at STP is heated to 250oC. What is the pressure at this temperature? What law was used?
22. 215 mL of air at a pressure of 352 mm Hg is compressed to a pressure of 725 mm Hg. What is the new volume?
Assume that the temperature is held constant. Which gas law applies?
23. A sample of gas at 22oC exerts a pressure of 1.00 atm. If the gas is heated to 100oC at constant volume, what
will be its new pressure in atmospheres? Which gas law applies?
24. Use the following data to find the new temperature: V1 = 45 L, T1 = 275 K, V2 = 12 L. Which gas law applies?
Answers: (19) 220 kPa, (20) 3.3 L, (21) 194 kPa, (22) 104 mL, (23) 1.26 atm, (24) 73 K,
M is the molar mass in g/mol
V is volume in liters
n is the number of moles
m is the mass in grams
T is temperature in Kelvin
Combined Gas Law: P ·V / T = k or P1·V1 / T1 = P2·V2 / T2
Molar Mass: M = mRT/PV
P is pressure in kPa
R = 8.31 kPaL/molK.
Ideal Gas Law: PV = nRT
Density: D = PM/RT
25. A meteorological balloon contains 250 L of helium at 22oC and 740 mm Hg. If the balloon can expand its volume
as it rises in the atmosphere, what volume will it occupy if it rises to an altitude where the temperature is -62oC
and the pressure is only 425 mm Hg? Use the combined gas law.
26. How many moles of air occupy 1.00 L at 23oC and 89.8 kPa?
27. What is the molar mass of a gas if 0.25 g occupies 125 mL at 28oC and 95.9 kPa?
28. Determine the density of hydrogen bromide gas at 340 kPa and 268 K.
29. What is the volume of 1.00 mol of any gas at STP?
30. How many moles of gas are present in a 2.0 L balloon at 22oC and 91.7 kPa?
31. What is the density of silicon tetrafluoride gas at 72oC and 144.5 kPa?
32. A sample of an unknown gas has a mass of 0.116 g. It occupies a volume of 25.0 mL at a temperature of 127 oC
and has a pressure of 155.3 kPa. Calculate the molar mass of the gas. Remember to convert any units to the
correct values if necessary.
33. Determine the mass of CO2 gas that has a volume of 7.10 L at a pressure of 89.8 kPa and a temperature of 31oC.
Hint: Solve the equation for m, and use the molar mass of CO2.
34. A gas has a density of 1.784 g/L at STP. What is its molar mass? What noble gas has this molar mass?
Use stoichiometric methods to solve the following problems…
35. Ammonia can react with oxygen to produce nitrogen and water according to the following equation: 4NH3(g) +
3O2(g) → 2N2(g) + 6H2O(l)
If 1.78 L of O2 reacts, what volume of nitrogen will be produced? Assume that temperature and pressure remain
constant.
36. Ethylene gas burns in air according to the following equation: C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(l)
If 13.8 L of C2H4 burns completely with oxygen, calculate the volume of CO2 produced, assuming that the
reactants and products are measured at the same pressure and temperature.
37. When arsenic(III) sulfide is roasted in air, it reacts with oxygen to produce arsenic (III) oxide and sulfur dioxide
according to the following equation: 2As2S3(s) + 9O2(g) → 2As2O3(s) + 6SO2(g)
When 89.5 g of As2S3 are roasted with excess oxygen, what volume of SO2 is produced? The gaseous product is
measured at 405 K and 98.0 kPa.
38. One gallon of gasoline has a mass of roughly 3500 g. Although gasoline is a mixture, it can be represented by
the equation: 2C8H18(g) + 25O2(g) → 16CO2(g) + 18H2O(g)
When one gallon of gasoline is burned, how many liters of carbon dioxide are produced at 22oC and 99 kPa?
39. What is the mass in kilograms of the carbon dioxide produced when a gallon of gasoline (3500 g or 3.5 kg) is
burned?
40. Based on your answer to the previous question, compare the mass of fuel to the mass of carbon dioxide
produced when a fuel is burned.
Answers: (25) 311 L, (26) 0.0365 mol, (27) 52 g/mol, (28) 12.3 g/L, (29) 22.4 L, (30) 0.075 mol, (31) 5.25 g/L, (32) 99.3
g/mol, (33) 11.1 g, (34) 39.9 g/mol is Argon, (35) 1.19 L, (36) 27.6 L, (37) 37.4 L, (38) 6100 L, (39) 11000 g = 11 kg of
CO2 for every gallon of gas burned; that is about 24 pounds!