Q: A sample of gas occupies 4.0 L at 2.0 atm. If the pressure is increased to 8.0 atm at constant temperature, what will be the new volume?

$$V_2$$ = \frac{$$P_1$$ $$V_1$$}{$$P_2$$} = \frac{2.0 \times 4.0}{8.0} = 1.0\ \text{L}$$

Q: A weather balloon is filled with 5.0 mol of helium at 1.0 atm and 273 K. What is its volume at these conditions?

$$V = \frac{nRT}{P} = \frac{5.0 \times 0.08206 \times 273}{1.0} = 112\ \text{L}$$

Q: A mixture contains 2.0 mol $$N_2$$ and 3.0 mol $$O_2 in a 10.0 L $$container at 300 K. What is the total pressure of the mixture?

$$P = \frac{nRT}{V} = \frac{5.0 \times 0.08206 \times 300}{10.0} = 12.3\ \text{atm}$$

Q: A 10.0 g sample of an unknown gas occupies 5.0 L at 2.0 atm and 300 K. What is the molar mass of the gas?

$$M = \frac{mRT}{PV} = \frac{10.0 \times 0.08206 \times 300}{2.0 \times 5.0} = 24.6\ \text{g/mol}$$

Q: A gas sample is collected over water at 25°C. The total pressure is 760 mmHg, and the vapor pressure of water at 25°C is 24 mmHg. What is the pressure of the dry gas?

$$P_{\text{gas}} = P_{\text{total}} - P$$_{\text{H}$$_2O} = 760 - 24 = 736\ \text{mmHg}$$

Question 1

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

Accepted Answer

Gas molecules are in continuous, random motion and occupy negligible volume compared to the container.

Question 2

A sample of gas occupies 4.0 L at 2.0 atm. If the pressure is increased to 8.0 atm at constant temperature, what will be the new volume?

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$}{$$P_2$$} = \frac{2.0 	imes 4.0}{8.0} = 1.0\ 	ext{L}$$

Question 3

Which of the following gases is most likely to behave non-ideally at low temperature and high pressure?

Accepted Answer

Ammonia ($$NH_3)$$

Question 4

A weather balloon is filled with 5.0 mol of helium at 1.0 atm and 273 K. What is its volume at these conditions?

Accepted Answer

$$V = \frac{nRT}{P} = \frac{5.0 	imes 0.08206 	imes 273}{1.0} = 112\ 	ext{L}$$

Question 5

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

Accepted Answer

$$\frac{r_1$}{r_2$} = \sqrt{\frac{M_2$}{M_1$}}$$, where $$r is $$the rate of effusion and $$M is $$molar mass.

Question 6

A mixture contains 2.0 mol $$N_2$$ and 3.0 mol $$O_2 in a 10.0 L $$container at 300 K. What is the total pressure of the mixture?

Accepted Answer

$$P = \frac{nRT}{V} = \frac{5.0 	imes 0.08206 	imes 300}{10.0} = 12.3\ 	ext{atm}$$

Question 7

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

Accepted Answer

Gas molecules are attracted to each other by strong forces.

Question 8

A 10.0 g sample of an unknown gas occupies 5.0 L at 2.0 atm and 300 K. What is the molar mass of the gas?

Accepted Answer

$$M = \frac{mRT}{PV} = \frac{10.0 	imes 0.08206 	imes 300}{2.0 	imes 5.0} = 24.6\ 	ext{g/mol}$$

Question 9

Which of the following gases will have the highest root-mean-square speed ($$u_{rms}) at 298 K$$?

Accepted Answer

Hydrogen ($$H_2)$$

Question 10

A gas sample is collected over water at 25°C. The total pressure is 760 mmHg, and the vapor pressure of water at 25°C is 24 mmHg. What is the pressure of the dry gas?

Accepted Answer

$$P_{	ext{gas}} = P_{	ext{total}} - P$$_{	ext{H}$$_2O} = 760 - 24 = 736\ 	ext{mmHg}$$

Question 11

Which of the following best describes the effect of increasing temperature on the pressure of a gas in a rigid container?

Accepted Answer

Pressure increases due to increased average kinetic energy and more frequent collisions.

Question 12

A 2.0 L flask contains a mixture of 0.5 mol $$H_2$$ and 1.0 mol $$N_2 at 300 K. $$What is the mole fraction of $$H_2$$?

Accepted Answer

$$X_{H_2$} = \frac{0.5}{0.5 + 1.0} = 0.33$$

Question 13

Which of the following is a correct unit conversion for standard atmospheric pressure?

Accepted Answer

$$1\ 	ext{atm} = 101,325\ 	ext{Pa}$$

Question 14

A gas has a density of $$1.96\ 	ext{g/L} at$$ $$2.00\ 	ext{atm}$$ and $$273\ 	ext{K}. $$What is its molar mass?

Accepted Answer

$$M = \frac{dRT}{P} = \frac{1.96 	imes 0.08206 	imes 273}{2.00} = 21.9\ 	ext{g/mol}$$

Question 15

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

Accepted Answer

It corrects for molecular volume and intermolecular attractions.

Question 16

A 1.0 L container holds 1.0 mol of $$CO_2 at 300 K. $$Calculate the pressure using the van der Waals equation ($$a = 3.59\ 	ext{L}^2\cdot	ext{atm}/	ext{mol}^2$$, $$b = 0.0427\ 	ext{L}/	ext{mol}).$$

Accepted Answer

$$\left(P + \frac{n^2$ a}{V^2$}ight)(V - nb) = nRT$$;\ $$P = \frac{nRT}{V - nb} - \frac{n^2$ a}{V^2$} = \frac{1.0 	imes 0.08206 	imes 300}{1.0 - 1.0 	imes 0.0427} - \frac{1.0^2$ 	imes 3.59}{1.0^2$} = 25.7 - 3.59 = 22.1\ 	ext{atm}$$

Chapter 10: Gases – Properties, Laws, and Real Behavior

Guida di studio - Domande di pratica

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