Q: A 250-mL flask contains CO$$_2$$ gas at 1.3 atm and 31 $$^ ext{o}C. $$How many moles of CO$$_2$$ were generated? (Use $$R = 0.08206 L-$$atm/mol-K)

$$n = \frac{(1.3)(0.250)}{0.08206 \times 304} = 0.013$$ mol

Q: What is the density of carbon tetrachloride vapor at 714 torr and 125 $$^ ext{o}C$$? (Molar mass = 153.82 g/mol, $$R = 62.36 L-$$torr/mol-K)

$$d = \frac{PM}{RT} = \frac{714 \times 153.82}{62.36 \times (125+273)} = 1.45 g/L$$

Q: A mixture of 6.00 g O$$_2$$ and 9.00 g CH$$_4 is $$placed in a 15.0-L vessel at 0 $$^ ext{o}C. $$What is the total pressure in the vessel? ($$R = 0.08206 L-$$atm/mol-K)

$$P_t = \frac{(0.188 + 0.562) \times 0.08206 \times 273}{15.0} = 0.89$$ atm

Q: A synthetic atmosphere contains 18.0 mol percent O$$_2$$ and the total pressure is 745 torr. What is the partial pressure of O$$_2$$?

$$P_{O_2$} = 0.18 \times 745 = 134$$ torr

Q: A gas sample at 1.5 atm and 25 $$^ ext{o}C is $$heated to 450 $$^ ext{o}C. $$What is the new pressure, assuming constant volume?

$$P_2$$ = $$P_1$$ \frac{$$T_2$$}{$$T_1$$} = 1.5 \times \frac{723}{298} = 3.64$$ atm

Question 1

Which of the following statements best explains why gases are compressible, according to the kinetic-molecular theory?

Accepted Answer

The combined volume of all gas molecules is negligible compared to the total container volume.

Question 2

A 250-mL flask contains CO$$_2$$ gas at 1.3 atm and 31 $$^	ext{o}C. $$How many moles of CO$$_2$$ were generated? (Use $$R = 0.08206 L-$$atm/mol-K)

Accepted Answer

$$n = \frac{(1.3)(0.250)}{0.08206 	imes 304} = 0.013$$ mol

Question 3

Which gas law describes the relationship between the volume and the number of moles of a gas at constant temperature and pressure?

Accepted Answer

Avogadro's Law

Question 4

A balloon filled with 6.0 L of air at 1.0 atm and 22 $$^	ext{o}C $$ascends to a region where the pressure is 0.45 atm and the temperature is -21 $$^	ext{o}C. $$What is the final volume of the balloon?

Accepted Answer

$$V_2$$ = \frac{$$V_1$$ $$P_1$$ $$T_2$$}{$$P_2$$ $$T_1$$} = \frac{6.0 	imes 1.0 	imes 252}{0.45 	imes 295} = 11.5$$ L

Question 5

Which of the following compounds is colorless and odorless, but toxic, as a gas at room temperature?

Accepted Answer

Carbon monoxide (CO)

Question 6

What is the density of carbon tetrachloride vapor at 714 torr and 125 $$^	ext{o}C$$? (Molar mass = 153.82 g/mol, $$R = 62.36 L-$$torr/mol-K)

Accepted Answer

$$d = \frac{PM}{RT} = \frac{714 	imes 153.82}{62.36 	imes (125+273)} = 1.45 g/L$$

Question 7

A mixture of 6.00 g O$$_2$$ and 9.00 g CH$$_4 is $$placed in a 15.0-L vessel at 0 $$^	ext{o}C. $$What is the total pressure in the vessel? ($$R = 0.08206 L-$$atm/mol-K)

Accepted Answer

$$P_t = \frac{(0.188 + 0.562) 	imes 0.08206 	imes 273}{15.0} = 0.89$$ atm

Question 8

According to Graham’s Law, which gas will effuse faster: helium (He) or argon (Ar)?

Accepted Answer

Helium, because it has a lower molar mass.

Question 9

A synthetic atmosphere contains 18.0 mol percent O$$_2$$ and the total pressure is 745 torr. What is the partial pressure of O$$_2$$?

Accepted Answer

$$P_{O_2$} = 0.18 	imes 745 = 134$$ torr

Question 10

Which of the following is NOT an assumption of the kinetic-molecular theory of gases?

Accepted Answer

Gas molecules exert attractive and repulsive forces on each other.

Question 11

If the pressure of a gas is doubled at constant temperature, what happens to its volume according to Boyle’s Law?

Accepted Answer

The volume is halved.

Question 12

Which equation represents the ideal-gas law?

Accepted Answer

$$PV = nRT$$

Question 13

A gas sample at 1.5 atm and 25 $$^	ext{o}C is $$heated to 450 $$^	ext{o}C. $$What is the new pressure, assuming constant volume?

Accepted Answer

$$P_2$$ = $$P_1$$ \frac{$$T_2$$}{$$T_1$$} = 1.5 	imes \frac{723}{298} = 3.64$$ atm

Question 14

Which of the following best describes effusion?

Accepted Answer

The escape of gas molecules through a tiny hole.

Question 15

What is the root-mean-square speed ($$u_{rms}) of O$_2$$ molecules at 25 $$^	ext{o}C$$? (Molar mass = 32.0 g/mol, $$R = 8.314 J/$$mol-K)

Accepted Answer

$$u_{rms} = \sqrt{\frac{3 	imes 8.314 	imes 298}{0.032}} = 484 m/s$$

Question 16

Which of the following gases will have the highest molecular speed at the same temperature?

Accepted Answer

He

Question 17

If 5.26 L of NH$$_3 is $$produced at STP, how many grams of N$$_2$$ are reacted? (Molar mass N$$_2 = 28.02 g/$$mol)

Accepted Answer

$$5.26 	imes \frac{1}{22.4} 	imes \frac{1}{2} 	imes 28.02 = 3.29 g$$

Question 18

Which of the following is a correct conversion for pressure units?

Accepted Answer

1 atm = 760 mm Hg = 760 torr = 101.325 kPa

Chemistry Chapter 10

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