Q: A sample of nitrogen gas occupies 10.0 L at 2.00 atm and 300 K. What will be its volume if the pressure is increased to 4.00 atm at constant temperature?

$$V_2$$ = \frac{P_1V_1}{$$P_2$$} = \frac{2.00 \times 10.0}{4.00} = 5.00\ \text{L}$$

Q: A 5.00 g sample of an unknown gas occupies 2.50 L at 1.00 atm and 27°C. What is the molar mass of the gas? (Use $$R = 0.0821\ \text{L} \cdot \text{atm} / \text{mol} \cdot \text{K})$$

$$M = \frac{mRT}{PV} = \frac{5.00 \times 0.0821 \times 300}{1.00 \times 2.50} = 49.3\ \text{g/mol}$$

Q: A 1.00 L flask contains 0.50 mol of He and 0.50 mol of Ne at 300 K. If the total pressure is 2.46 atm, what is the partial pressure of Ne?

$$P_{Ne} = X_{Ne} \times P_{total} = 0.50 \times 2.46 = 1.23\ \text{atm}$$

Question 1

A weather balloon is released at sea level where the atmospheric pressure is 1 atm and the temperature is 25°C. As the balloon rises, the external pressure decreases while the temperature remains constant. According to Boyle’s Law, what happens to the volume of the balloon as it ascends?

Accepted Answer

The volume increases because pressure decreases. $$P_1V_1 = P_2V_2$$

Question 2

Which of the following statements best explains why gases are highly compressible compared to solids and liquids?

Accepted Answer

Gas molecules occupy a negligible fraction of the total volume, allowing them to be compressed easily.

Question 3

A sample of nitrogen gas occupies 10.0 L at 2.00 atm and 300 K. What will be its volume if the pressure is increased to 4.00 atm at constant temperature?

Accepted Answer

$$V_2$$ = \frac{P_1V_1}{$$P_2$$} = \frac{2.00 	imes 10.0}{4.00} = 5.00\ 	ext{L}$$

Question 4

Which of the following is the correct mathematical expression for Charles’s Law?

Accepted Answer

$$\frac{V_1$}{T_1$} = \frac{V_2$}{T_2$}$$

Question 5

A 5.00 g sample of an unknown gas occupies 2.50 L at 1.00 atm and 27°C. What is the molar mass of the gas? (Use $$R = 0.0821\ 	ext{L} \cdot 	ext{atm} / 	ext{mol} \cdot 	ext{K})$$

Accepted Answer

$$M = \frac{mRT}{PV} = \frac{5.00 	imes 0.0821 	imes 300}{1.00 	imes 2.50} = 49.3\ 	ext{g/mol}$$

Question 6

Which of the following best describes Dalton’s Law of Partial Pressures?

Accepted Answer

The total pressure of a mixture of gases is the sum of the partial pressures of each gas: $$P_t = P_1$ + P_2$ + P_3$ + \ldots$$

Question 7

A mixture contains 2.0 mol of O$$_2$$ and 3.0 mol of N$$_2 in a 10.0 L $$container at 300 K. What is the mole fraction of O$$_2 in $$the mixture?

Accepted Answer

$$X_{O_2$} = \frac{2.0}{2.0 + 3.0} = 0.40$$

Question 8

According to the kinetic-molecular theory, which of the following statements is NOT correct for an ideal gas?

Accepted Answer

Attractive and repulsive forces between gas molecules are significant.

Question 9

Which gas will effuse fastest through a small hole at the same temperature and pressure: H$$_2$$, O$$_2$$, N$$_2$$, or CO$$_2$$?

Accepted Answer

H$$_2$$

Question 10

A 1.00 L flask contains 0.50 mol of He and 0.50 mol of Ne at 300 K. If the total pressure is 2.46 atm, what is the partial pressure of Ne?

Accepted Answer

$$P_{Ne} = X_{Ne} 	imes P_{total} = 0.50 	imes 2.46 = 1.23\ 	ext{atm}$$

Question 11

Which of the following conditions would cause a real gas to deviate most from ideal behavior?

Accepted Answer

Low temperature and high pressure

Question 12

A sample of gas has a density of 1.96 g/L at 2.00 atm and 273 K. What is the molar mass of the gas? (Use $$R = 0.0821\ 	ext{L} \cdot 	ext{atm} / 	ext{mol} \cdot 	ext{K})$$

Accepted Answer

$$M = \frac{dRT}{P} = \frac{1.96 	imes 0.0821 	imes 273}{2.00} = 21.9\ 	ext{g/mol}$$

Question 13

Which of the following best explains why the van der Waals equation is used for real gases?

Accepted Answer

It accounts for the attractive and repulsive forces between gas molecules and the finite volume of molecules.

Question 14

A reaction produces 2.00 L of CO$$_2$$ gas at STP. How many grams of CO$$_2$$ are produced? (Molar mass of CO$$_2 = 44.0 g/$$mol, 1 mol gas at STP = 22.4 L)

Accepted Answer

$$n = \frac{2.00}{22.4} = 0.0893\ 	ext{mol};\ m = 0.0893 	imes 44.0 = 3.93\ 	ext{g}$$

Question 15

Which of the following is the correct expression for the root-mean-square speed ($$u_{rms}) of a $$gas molecule?

Accepted Answer

$$u_{rms} = \sqrt{\frac{3RT}{M}}$$

Question 16

A gas sample is collected over water at 25°C and 1.00 atm total pressure. The vapor pressure of water at 25°C is 0.0313 atm. What is the partial pressure of the dry gas?

Accepted Answer

$$P_{gas} = P_{total} - P_{H_2O} = 1.00 - 0.0313 = 0.9687\ 	ext{atm}$$

Question 17

Which of the following best describes Graham’s Law of Effusion?

Accepted Answer

The rate of effusion of a gas is inversely proportional to the square root of its molar mass: $$	ext{Rate} \propto \frac{1}{\sqrt{M}}$$

Question 18

A 10.0 L container holds 1.00 mol of an ideal gas at 300 K. What is the pressure inside the container? (Use $$R = 0.0821\ 	ext{L} \cdot 	ext{atm} / 	ext{mol} \cdot 	ext{K})$$

Accepted Answer

$$P = \frac{nRT}{V} = \frac{1.00 	imes 0.0821 	imes 300}{10.0} = 2.46\ 	ext{atm}$$

Chapter 10: Gases – Properties, Laws, and Theories

Guida di studio - Domande di pratica

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