1. Chapter 12 Gases

2. What is the pressure of the gas in the bulb? 1. P gas = P h 2. P gas = P atm 3. P gas = P h + P atm 4. P gas = P h - P atm 5. P gas = P atm - P h

3. What is the pressure of the gas in the bulb? 1. P gas = P h 2. P gas = P atm 3. P gas = P h + P atm 4. P gas = P h - P atm 5. P gas = P atm - P h

4. If 250 mL of NO is placed in a flask with O 2, what volume of O 2 is needed for complete reaction? 1.100 mL 2.125 mL 3.200 mL 4.250 mL 5.Cannot be determined from the given information. 2 NO (g) + O 2 (g) 2 NO 2 (g)

5. If 250 mL of NO is placed in a flask with O 2, what volume of O 2 is needed for complete reaction? 1.100 mL 2.125 mL 3.200 mL 4.250 mL 5.Cannot be determined from the given information. 2 NO (g) + O 2 (g) 2 NO 2 (g)

6. If an equal mass of each gas is put into a separate balloon, which will have the greatest volume? Assume that they are all the same temperature and pressure. 1.He 2.H 2 3.N 2 4.Ne 5.O 2

7. If an equal mass of each gas is put into a separate balloon, which will have the greatest volume? Assume that they are all the same temperature and pressure. 1.He 2.H 2 3.N 2 4.Ne 5.O 2

8. If equal masses of CH 4, C 2 H 6, and C 3 H 8 are placed in a flask, which of the following is true? 1. P CH 4 = P C 2 H 6 = P C 3 H 8 2. P CH 4 ~ P C 2 H 6 ~ P C 3 H 8 3. P CH 4 > P C 2 H 6 > P C 3 H 8 4. P CH 4 < P C 2 H 6 < P C 3 H 8 5. None of the above

9. If equal masses of CH 4, C 2 H 6, and C 3 H 8 are placed in a flask, which of the following is true? 1. P CH 4 = P C 2 H 6 = P C 3 H 8 2. P CH 4 ~ P C 2 H 6 ~ P C 3 H 8 3. P CH 4 > P C 2 H 6 > P C 3 H 8 4. P CH 4 < P C 2 H 6 < P C 3 H 8 5. None of the above

10. Arrange the gases according to increasing molecular speed. 1.He (25) < He (100) < Ne (25) < Ne (0) 2.He (25) < He (100) < Ne (0) < Ne (25) 3.Ne (0) < Ne (25) < He (25) < He (100) 4.Ne (25) < Ne (0) < He (100) < He (25) 5.Ne (0) < He (25) < Ne (25) < He (100) He (25°C) He (100°C) Ne (25°C) Ne (0°C)

11. Arrange the gases according to increasing molecular speed. 1.He (25) < He (100) < Ne (25) < Ne (0) 2.He (25) < He (100) < Ne (0) < Ne (25) 3.Ne (0) < Ne (25) < He (25) < He (100) 4.Ne (25) < Ne (0) < He (100) < He (25) 5.Ne (0) < He (25) < Ne (25) < He (100) He (25°C) He (100°C) Ne (25°C) Ne (0°C)

12. If a mixture of gas A and gas B is moved from flask 1 to flask 2, which of the following is true: 1. P A, P B, and P tot decrease 2. P A, P B, and P tot increase 3. P A and P B decrease, P tot remains the same 4. P A, P B, and P tot remain the same 5. P A and P B remain the same, P tot decreases flask 1flask 2

13. If a mixture of gas A and gas B is moved from flask 1 to flask 2, which of the following is true: 1. P A, P B, and P tot decrease 2. P A, P B, and P tot increase 3. P A and P B decrease, P tot remains the same 4. P A, P B, and P tot remain the same 5. P A and P B remain the same, P tot decreases flask 1flask 2

14. A gas initially at 2.0 atm is in an adjustable volume container of 10. L in volume. If the pressure is decreased to 0.50 atm, what is the new volume? 1.40. L 2.20. L 3.10. L 4.5.0 L

15. Correct Answer: P V 1 constant  Thus, 2.00 atm(10. L) = 0.50 atm (V final ) V final = 2.00 atm(10. L)/0.50 atm = 40. L 1.40. L 2.20. L 3.10. L 4.5.0 L

16. Assuming pressure is held constant, to what volume will a balloon initially at 1.0 L change if its temperature is decreased from 300 K to 75 K? 1.1.0 L 2.2.0 L 3.0.25 L 4.4.0 L

17. Correct Answer: TV   constant Thus, 1.0 L/300 K = (V final )/75 K V final = 75 K/(1.0 L)300 K = 0.25 L 1.1.0 L 2.2.0 L 3.0.25 L 4.4.0 L

18. At standard temperature and pressure, how many moles of gas are present in a box with a volume of 112 L? 1.1.00 moles 2.2.00 moles 3.5.00 moles 4.0.200 moles

19. Correct Answer:  L 22.41 atm 1.000 K 273.15KL·atm/mol· 0.08206mol 1   P nRT V PV Thus, at STP 22.41 L = 112 L 1.00 mol n n = 5.00 moles 1.1.00 moles 2.2.00 moles 3.5.00 moles 4.0.200 moles

20. At standard temperature and pressure, a hot-air balloon is filled with helium only to a volume of 4480 L. How many grams of helium are needed to fill the balloon? 1.200. g 2.400. g 3.800. g 4.50.0 g

21. Correct Answer: At STP 22.41 L = 4480 L 1.00 mol n n = 200. moles Since MW(He) is 4.0 g/mol Mass = (200. g)(4.0 g/mol) = 800. g 1.200. g 2.400. g 3.800. g 4.50.0 g

22. A gas sample occupies a volume of 4.00 L at 20°C. The temperature at which the gas would double its volume is 1.10°C 2.40°C 3.288°C 4.313°C

23. Correct Answer: The temperature scale is absolute, however; V initial / (V final ) = T final / (T initial ) 2 = T final / 293 K T final = 586 K, or 313°C 1.10°C 2.40°C 3.288°C 4.313°C

24. N 2 (g) + 3 H 2 (g) 2 NH 3 (g) At STP, 16 L of N 2 and 48 L of H 2 are mixed. Assuming all the reactants are consumed, how many L of NH 3 will be produced? 1.8.0 L 2.16 L 3.24 L 4.32 L 5.64 L

25. Correct Answer: According to Avogadro’s law, mole ratios in the chemical equation will be volume ratios under identical conditions. Because the reactants are in a stoichiometric 3:1 volume ratio, the product will have stoichiometric equivalence. Thus, (16 L N 2 )(2 mol NH 3 /1 mol N 2 ) = 32 L NH 3 )(constant TP,nV  1.8.0 L 2.16 L 3.24 L 4.32 L 5.64 L

26. A container holds a mixture of oxygen, neon, and helium gases whose partial pressures are 150 torr, 300 torr, and 450 torr, respectively. The mole fraction of neon is 1.0.17 2.0.33 3.0.50 4.0.67 totali PP i  

27. Correct Answer: X i = P i /P total X i = (300 torr)/(150 + 300 + 450) torr X i = 300 torr/900 torr = 0.33 totali PP i   1.0.17 2.0.33 3.0.50 4.0.67

28. A sample of He gas initially at STP is compressed to a smaller volume at constant temperature. What effect does this have on the rms speed of the atoms? 1.Increases 2.Decreases 3.No effect

29. Correct Answer: The rms speed is directly proportional to the square root of the temperature, which does not change in this example. 1.Increases 2.Decreases 3.No effect

30. An unknown gas effuses at half the rate of helium. This gas is likely to be which of the following? 1.H 2 2.CH 4 3.Ne 4.O 2 5.Ar

31. Correct Answer: (r 1 / 2 ) 2 =M 2 /M 1 M 2 = (r 1 /r 2 ) 2 M 1 M 2 = (2/1) 2 (4.0 g/mol) = 16.0 g/mol Therefore it could be CH 4 1.H 2 2.CH 4 3.Ne 4.O 2 5.Ar

32. Real gases deviate from ideal behavior at __________ and _________. 1.High temperature; low pressure 2.Low temperature; high pressure 3.High temperature; high pressure 4.Low temperature; low pressure

33. Correct Answer: At low temperature and high pressure, intermolecular forces increase as the molecules get closer together. 1.High temperature; low pressure 2.Low temperature; high pressure 3.High temperature; high pressure 4.Low temperature; low pressure