AP chem Review - 4 Name: ____________________ Text: chapter 5 & 10 (Gases)

© S. O’Malley 2012

• P1V1/T1 = P2V2/T2 • urms = (3RT/M)½ • PV = nRT • r1/r2 = (MM2/MM1)½ • KE = (3/2)RT • Pa = χaPT (Dalton’s law)

PROBLEMS 1. A sample of argon gas is sealed in

a container. The volume of the container is doubled. If the pressure remains constant, what happens to the absolute temperature? a. It does not change. b. It is halved. c. It is doubled. d. It is squared. e. It cannot be predicted.

2. A sealed, rigid container is filled with three ideal gases: A, B, and C. The partial pressure of each gas is known. The temperature and volume of the system are known. What additional information is needed to determine the masses of the gases in the container? a. the average distance traveled

between molecular collisions b. the intermolecular forces c. the volume of the gas

molecules d. the total pressure e. the molar masses of the gases

3. Two balloons are at the same temperature and pressure. One contains 14 g of nitrogen and the other contains 20.0 g of argon. Which statement is FALSE? a. The density of the nitrogen

sample is less than the density of the argon sample.

b. The average speed of the nitrogen molecules is the same as the average speed of the argon molecules.

c. The average kinetic energy of the nitrogen molecules is the same as the average kinetic energy of the argon molecules.

d. The volume of the nitrogen container is the same as the volume of the argon container.

e. The number of molecules in the nitrogen container is the same as the number of atoms in the argon container.

4. An experiment to determine the molecular mass of a gas begins by heating a solid to produce a gaseous product. The gas passes through a tube and displaces water in an inverted, water-filled bottle. Which of the following necessary

items may be determined after the experiment is completed? a. vapor pressure of water b. temperature of displaced water c. room barometric pressure d. mass of the solid used e. volume of the displaced water

5. The true volume of a particular real

gas is larger than that calculated from the ideal gas equation. This occurs because the ideal gas equation does NOT correct for the: a. attraction between molecules b. shape of the molecules c. volume of the molecules d. mass of the molecules e. speed of molecules

6. Aluminum metal reacts with HCl to

produce aluminum chloride and hydrogen gas. How many grams of aluminum must be added to an excess of HCl to produce 33.6 L of hydrogen gas, if the gas is at STP? a. 18.0 g b. 35.0 g c. 27.0 g d. 4.50 g e. 9.00 g

7. A reaction produces a gaseous

mixture of carbon dioxide, carbon monoxide, and water vapor. After one reaction, the mixture was analyzed and found to contain 0.60 mol of carbon dioxide, 0.30 mol of carbon monoxide, and 0.10 mol of water vapor. If the total pressure of the mixture was 0.80 atm, what was the partial pressure of the carbon monoxide? a. 0.080 atm b. 0.34 atm c. 0.13 atm d. 0.24 atm e. 0.48 atm

8. A sample of methane gas was

collected over water at 35oC. The sample was found to have a total pressure of 756 mmHg. Determine the partial pressure of the methane gas in the sample (vapor pressure of water at 35oC is 41 mmHg). a. 760 mmHg b. 41 mmHg c. 715 mmHg d. 797 mmHg

e. 756 mmHg

9. A sample of oxygen gas with a volume of 8.00 L at 127oC and 775 mmHg is heated until it expands to a volume of 20.00 L. Determine the final temperature of the oxygen gas, if the pressure remains constant. a. 727oC b. 318oC c. 1000oC d. 160oC e. 45oC

10. The average kinetic energy of

nitrogen molecules changes by what factor when the temperature is increased from 30oC to 60oC? a. (333 / 303) b. 2 c. ½ d. (303 / 333)½ e. 28

11. A 1.15-mol sample of carbon

monoxide gas has a temperature of 27oC and a pressure of 0.300 atm. If the temperature is lowered to 17oC, at constant volume, what would be the new pressure? a. 0.290 atm b. 0.519 atm c. 0.206 atm d. 0.338 atm e. 0.310 atm

12. An ideal gas sample weighing 1.28

grams at 127oC and 1.00 atm has a volume of 0.250 L. Determine the molar mass of the gas. a. 322 g/mol b. 168 g/mol c. 0.00621 g/mol d. 80.5 g/mol e. 49.4 g/mol

13. Increasing the temperature of an

ideal gas from 50 to 75oC at constant volume will cause which of the following to increase for the gas?

i. average distance between molecules ii. average speed of the molecules iii. average molecular mass of the gas

a. iii only b. i only c. ii only d. ii and iii e. i and ii

Problems taken from “5 Steps to a 5”, McGraw Hill

14. If a sample of CH4 effuses at a rate of 9.0 mol per hour at 35oC, which of the gases below will effuse at approximately twice the rate under the same conditions? a. CO b. He c. O2 d. F2 e. SiH4

15. A steel tank containing argon gas

has additional argon gas pumped into it at constant temperature. Which of the following is true for the gas in the tank? a. There is no change in the

number of gas atoms. b. There is an increase in the

volume of the gas. c. There is a decrease in the

pressure exerted by the gas. d. The gas atoms travel with the

same average speed. e. The gas atoms are separated

by a greater average distance

16. 2N2O5(s) → 4NO2(g) + O2(g) A 2 L evacuated flask has a 0.2 mol sample of N2O5(s) sealed inside it. The flask is heated to decompose

the solid and cooled to 300 K. The N2O5(s) is completely decomposed according to the balanced equation above. What is the nearest value to the final total pressure of the gases in the flask? (The value of the gas constant, R, is 0.082 L�atm/mol�K) a. 0.6 atm b. 6 atm c. 0.05 atm d. 1.2 atm e. 3 atm

17. A glass container is filled at room

temperature with equal numbers of moles of H2(g), O2(g), and NO2(g). The gases slowly leak out through a pinhole. After some of the gas has effused, which of the following is true of the relative values for the partial pressures of the gases remaining in the container? a. H2 < NO2 < O2 b. NO2 < H2 < O2 c. H2 = NO2 = O2 d. O2 < NO2 < H2 e. H2 < O2 < NO2

18. Which gas shows the greatest

deviation from ideal behavior? a. He

b. O2 c. SF4 d. SiH4 e. Ar

19. Determine the formula for a

gaseous silane (SinH2n+2) if it has a density of 5.47 g/L at 0oC and 1.00 atm. a. SiH4 b. Si2H6 c. Si3H8 d. Si4H10 e. Si5H12

20. Which of the following best explains why a hot-air balloon rises? a. The heating of the air causes

the pressure of the balloon to increase.

b. The cool outside air pushes the balloon higher.

c. The temperature difference between the inside and outside air causes convection currents.

d. Hot air has a lower density than cold air.

e. Cooler air diffuses more slowly than the wamer air.

FREE-RESPONSE 21. A hydrogen gas sample is collected over water. The volume of the sample was 190.0 mL at 26oC, and the pressure in the

room was 754 mmHg. The vapor pressure of water at 26oC is 25.2 mmHg. a. Calculate the number of moles of hydrogen in the sample. b. Calculate how many molecules of water vapor are present in the sample. c. Determine the density (in g/L) of the gas mixture. d. Determine the mole fraction of water.

22. A sample containing 2/3 mole of potassium chlorate, KClO3, is heated until it decomposes to potassium chloride and

oxygen gas. The oxygen is collected in an inverted bottle through the displacement of water. Answer the following questions using this information. a. Write a balanced chemical equation for the reaction. b. How many moles of oxygen gas are produced? c. The temperature and pressure of the sample are adjusted to STP. The volume of the sample is found to be slightly

greater than 22.4 liters. Explain. d. An excess of sulfur is burned in the oxygen. Write a balanced chemical equation and calculate the number of moles

of gas formed. e. After the sulfur had completely reacted, a sample of the residual water was removed from the bottle and found to be

acidic. Explain.

21. a. 0.00742 mol H2 b. 1.55 x 1020 molecules c. 0.103 g/L d. 0.0335 22. a. 2KClO3(s) → 2KCl(s) + 3O2(g) b. 1 mole O2 c. At STP the volume of 1 mole of O2 should be 22.4 liters. The volume is greater because oxygen was not the only gas in the sample. H2O vapor was present. The presence of the additional gas leads to a larger volume. d. S(s) + O2(g) → SO2(g), 1 mol SO2 is produced… OR… 2S(s) + 3O2(g) → 2SO3(g), 2/3 mol SO3 produced e. Either of the sulfur oxides (SO2 or SO3) will dissolve in water to produce an acid (H2SO3 or H2SO4, respectively).

1. C 2. E 3. B 4. A 5. C 6. C 7. D 8. C 9. A 10. A 11. A 12. B 13. C 14. B 15. D 16. B 17. E 18. C 19. D 20. D