Q: A sample of gas has a volume of 2.80 L at an unknown temperature. When the sample is submerged in ice water at $$t = 0\ ^\circ\text{C}$$, its volume decreases to 2.57 L. What was its initial temperature in kelvins? (Assume constant pressure.)

$$T_1$$ = \frac{$$V_1$$}{$$V_2$$} \times $$T_2$$ = \frac{2.80}{2.57} \times 273 = 297\ \text{K}$$

Q: A mixture of helium, neon, and argon has a total pressure of 558 mm Hg. If the partial pressure of helium is 341 mm Hg and the partial pressure of neon is 112 mm Hg, what is the partial pressure of argon?

$$P_{\text{Ar}} = 558\ \text{mm Hg} - 341\ \text{mm Hg} - 112\ \text{mm Hg} = 105\ \text{mm Hg}$$

Q: A 4.8-L sample of helium gas contains 0.22 mol of helium. How many additional moles of helium gas should you add to obtain a volume of 6.4 L at constant temperature and pressure?

$$n_2$$ = \frac{$$V_2$$}{$$V_1$$} \times $$n_1$$ = \frac{6.4}{4.8} \times 0.22 = 0.29\ \text{mol}$$; Additional moles = 0.29 - 0.22 = 0.07$$\ \text{mol}$$

Q: What is the partial pressure of oxygen that a diver breathes with a heliox mixture containing 2.0% oxygen at a depth of 90 m where the total pressure is 10.0 atm?

$$P_{\text{O}_2$$} = \text{Fractional composition} \times \text{Total pressure} = 0.02 \times 10.0 = 0.20\ \text{atm}$$

Question 1

Which statement best explains why gases are compressible, according to the kinetic molecular theory?

Accepted Answer

Gases are compressible because there is a lot of empty space between gas particles.

Question 2

A scuba diver at a depth of 20 m breathes air at a pressure of 3 atm. If the diver holds their breath and ascends to the surface (1 atm), what happens to the volume of air in their lungs, according to Boyle’s law?

Accepted Answer

The volume increases by a factor of 3.

Question 3

What is the SI unit of pressure, and how is it defined?

Accepted Answer

The SI unit of pressure is the pascal (Pa), defined as $$1\ 	ext{N}/	ext{m}^2.$$

Question 4

According to the kinetic molecular theory, what happens to the average kinetic energy of gas particles as the temperature increases?

Accepted Answer

The average kinetic energy increases.

Question 5

A sample of gas has a volume of 2.80 L at an unknown temperature. When the sample is submerged in ice water at $$t = 0\ ^\circ	ext{C}$$, its volume decreases to 2.57 L. What was its initial temperature in kelvins? (Assume constant pressure.)

Accepted Answer

$$T_1$$ = \frac{$$V_1$$}{$$V_2$$} 	imes $$T_2$$ = \frac{2.80}{2.57} 	imes 273 = 297\ 	ext{K}$$

Question 6

Which 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 7

A mixture of helium, neon, and argon has a total pressure of 558 mm Hg. If the partial pressure of helium is 341 mm Hg and the partial pressure of neon is 112 mm Hg, what is the partial pressure of argon?

Accepted Answer

$$P_{	ext{Ar}} = 558\ 	ext{mm Hg} - 341\ 	ext{mm Hg} - 112\ 	ext{mm Hg} = 105\ 	ext{mm Hg}$$

Question 8

What is the ideal gas law equation, and what does each variable represent?

Accepted Answer

$$PV = nRT$$, where $$P is $$pressure, $$V is $$volume, $$n is $$moles, $$R is $$the gas constant, and $$T is $$temperature in kelvins.

Question 9

A 4.8-L sample of helium gas contains 0.22 mol of helium. How many additional moles of helium gas should you add to obtain a volume of 6.4 L at constant temperature and pressure?

Accepted Answer

$$n_2$$ = \frac{$$V_2$$}{$$V_1$$} 	imes $$n_1$$ = \frac{6.4}{4.8} 	imes 0.22 = 0.29\ 	ext{mol}$$; Additional moles = 0.29 - 0.22 = 0.07$$\ 	ext{mol}$$

Question 10

A sample of gas has a mass of 0.136 g, a volume of 0.112 L, a temperature of 298 K, and a pressure of 1.06 atm. What is its molar mass?

Accepted Answer

First, use the ideal gas law: $$n = \frac{PV}{RT}$$, then $$	ext{Molar mass} = \frac{	ext{mass}}{n}$$. $$n = \frac{1.06 	imes 0.112}{0.0821 	imes 298} = 0.0049\ 	ext{mol}$$; Molar mass $$= \frac{0.136}{0.0049} = 27.8\ 	ext{g/mol}$$

Question 11

What is the partial pressure of oxygen that a diver breathes with a heliox mixture containing 2.0% oxygen at a depth of 90 m where the total pressure is 10.0 atm?

Accepted Answer

$$P_{	ext{O}_2$$} = 	ext{Fractional composition} 	imes 	ext{Total pressure} = 0.02 	imes 10.0 = 0.20\ 	ext{atm}$$

Question 12

Why is it impossible to drink from a straw longer than about 10.3 meters, even if the straw is perfectly sealed and rigid?

Accepted Answer

Because the pressure exerted by the atmosphere can only support a column of water up to 10.3 meters high.

Question 13

A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. If the pressure is decreased to 1.0 atm, what is the new volume?

Accepted Answer

$$P_1V_1 = P_2V_2 \Rightarrow V_2$ = \frac{P_1V_1}{P_2$} = \frac{4.0 	imes 6.0}{1.0} = 24.0\ 	ext{L}$$

Question 14

Which property of gases allows hot air balloons to rise?

Accepted Answer

Hot air balloons rise because heating the air decreases its density, allowing it to float in cooler, denser air.

Question 15

What is the molar volume of an ideal gas at standard temperature and pressure (STP)?

Accepted Answer

22.4 L

Question 16

Which of the following is a major gaseous air pollutant that is a lung and eye irritant and a precursor of acid rain?

Accepted Answer

Sulfur dioxide ($$	ext{SO}_2)$$

Study Guide: Properties and Laws of Gases (Chapter 11)

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