Q: A sample of chlorine gas occupies 946 mL at 726 mmHg. If the volume is reduced to 154 mL at constant temperature, what is the final pressure in mmHg?

$$P_2$$ = \frac{$$P_1$$ $$V_1$$}{$$V_2$$} = \frac{726 \times 946}{154} = 4460$$ mmHg

Q: What is the volume (in liters) occupied by 2.12 moles of NO gas at 6.54 atm and 76°C?

$$V = \frac{nRT}{P} = \frac{2.12 \times 0.082 \times (273+76)}{6.54} = 9.3 L$$

Q: Calculate the density (in g/L) of uranium hexafluoride (UF$$_6) at 779 $$mmHg and 62°C. (Molar mass = 352 g/mol)

$$d = \frac{P \times M}{R \times T} = \frac{1.025 \times 352}{0.082 \times 335} = 13.2 g/L$$

Q: A sample of natural gas contains 8.24 moles of methane, 0.421 mole of ethane, and 0.116 mole of propane. If the total pressure is 1.37 atm, what is the partial pressure of ethane?

$$P_{ethane} = X_{ethane} \times P_{total} = \frac{0.421}{8.24+0.421+0.116} \times 1.37 = 0.064$$ atm

Q: What is the root-mean-square (rms) speed of nitrogen molecules ($$N_2) at 250 K$$? (Molar mass $$N_2 = 0.028$ kg/mol, R = 8.314$ J/mol·K)

$$u_{rms} = \sqrt{\frac{3RT}{M}} = \sqrt{\frac{3 \times 8.314 \times 250}{0.028}} = 463 m/s$$

Question 1

Which of the following statements best explains why gases are the most compressible state of matter?

Accepted Answer

Gas molecules are far apart compared to their size, allowing them to be squeezed closer together.

Question 2

A sample of chlorine gas occupies 946 mL at 726 mmHg. If the volume is reduced to 154 mL at constant temperature, what is the final pressure in mmHg?

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$}{$$V_2$$} = \frac{726 	imes 946}{154} = 4460$$ mmHg

Question 3

Which instrument is used to measure atmospheric pressure?

Accepted Answer

Barometer

Question 4

What is the volume (in liters) occupied by 2.12 moles of NO gas at 6.54 atm and 76°C?

Accepted Answer

$$V = \frac{nRT}{P} = \frac{2.12 	imes 0.082 	imes (273+76)}{6.54} = 9.3 L$$

Question 5

Which law states that at constant pressure, the volume of a gas is proportional to its absolute temperature?

Accepted Answer

Charles's Law

Question 6

A gaseous compound is 78.14% boron and 21.86% hydrogen. At 27°C, 74.3 mL of the gas exerts a pressure of 1.12 atm. If the mass of the gas is 0.0934 g, what is its molar mass?

Accepted Answer

$$M = \frac{mass}{n} = \frac{0.0934}{\frac{PV}{RT}} = \frac{0.0934}{\frac{1.12 	imes 0.0743}{0.082 	imes 300}} = 30.0 g/$$mol

Question 7

Which of the following is NOT a postulate of the kinetic molecular theory of gases?

Accepted Answer

Gas particles attract and repel each other strongly.

Question 8

Calculate the density (in g/L) of uranium hexafluoride (UF$$_6) at 779 $$mmHg and 62°C. (Molar mass = 352 g/mol)

Accepted Answer

$$d = \frac{P 	imes M}{R 	imes T} = \frac{1.025 	imes 352}{0.082 	imes 335} = 13.2 g/L$$

Question 9

A gas initially at 4.0 L, 1.2 atm, and 66°C undergoes changes so that its final volume and temperature become 1.7 L and 42°C. What is its final pressure?

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$T_1$$ $$V_2$$} = \frac{1.2 	imes 4.0 	imes (273+42)}{(273+66) 	imes 1.7} = 1.62$$ atm

Question 10

Which equation correctly expresses Dalton’s Law of Partial Pressures for a mixture of gases?

Accepted Answer

$$P_{total} = P_1$ + P_2$ + P_3$ + \ldots$$

Question 11

A sample of natural gas contains 8.24 moles of methane, 0.421 mole of ethane, and 0.116 mole of propane. If the total pressure is 1.37 atm, what is the partial pressure of ethane?

Accepted Answer

$$P_{ethane} = X_{ethane} 	imes P_{total} = \frac{0.421}{8.24+0.421+0.116} 	imes 1.37 = 0.064$$ atm

Question 12

What is the root-mean-square (rms) speed of nitrogen molecules ($$N_2) at 250 K$$? (Molar mass $$N_2 = 0.028$ kg/mol, R = 8.314$ J/mol·K)

Accepted Answer

$$u_{rms} = \sqrt{\frac{3RT}{M}} = \sqrt{\frac{3 	imes 8.314 	imes 250}{0.028}} = 463 m/s$$

Question 13

641 mL of hydrogen gas is collected at 30°C and a pressure of 749 mmHg. The pressure of water vapor at 30°C is 31.82 mmHg. What is the mass of hydrogen gas collected?

Accepted Answer

$$P_{H_2$} = 749 - 31.82 = 717.18$$ mmHg; $$n = \frac{PV}{RT}$$; $$mass = n 	imes 2.016 g/$$mol; $$mass = 0.075 g$$

Question 14

Which of the following best describes the relationship between the average kinetic energy of gas particles and temperature?

Accepted Answer

Average kinetic energy is directly proportional to the absolute temperature.

Question 15

A 2.14-L sample of hydrogen chloride gas at 2.61 atm and 28°C is completely dissolved in 668 mL of water. What is the molarity of the resulting hydrochloric acid solution?

Accepted Answer

$$n = \frac{PV}{RT} = \frac{2.61 	imes 2.14}{0.082 	imes 301} = 0.23$$ mol; $$M = \frac{0.23}{0.668} = 0.34 M$$

Question 16

Assuming no change in temperature and pressure, how many liters of $$O_2$$ are required for the complete combustion of 14.9 L of $$C_4H_{10}$$? (Reaction: $$2C_4H_{10} + 13O_2 \rightarrow 8CO_2 + 10H_2O)$$

Accepted Answer

$$O_2 = 14.9$$ 	imes \frac{13}{2} = 96.85$$ L

Question 17

Which of the following gases will have the highest root-mean-square (rms) speed at the same temperature?

Accepted Answer

Hydrogen ($$H_2)$$

Study Notes: Properties and Laws of Gases (Handout 5, Chapter 7)

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