Q: At STP, what is the volume occupied by 2 moles of an ideal gas?

$$2 \text{ mol} \times 22.4 \text{ L/mol} = 44.8 \text{ L}$$

Q: A gas sample contains 0.552 mol at 305 K in a 12.0 L container. What is the pressure in atm?

$$P = \frac{nRT}{V} = \frac{0.552 \times 0.08206 \times 305}{12.0} = 1.15 \text{ atm}$$

Question 1

Which of the following best explains why the pressure inside a bicycle tire increases when more air is pumped into it, assuming the temperature and volume remain constant?

Accepted Answer

The concentration of gas molecules increases, leading to more collisions with the tire walls.

Question 2

A sample of gas occupies 4.00 L at 1.00 atm. If the volume is decreased to 2.00 L at constant temperature, what is the new pressure?

Accepted Answer

$$P_1V_1 = P_2V_2$$; $$P_2$$ = \frac{P_1V_1}{$$V_2$$} = \frac{1.00 	ext{ atm} 	imes 4.00 	ext{ L}}{2.00 	ext{ L}} = 2.00 	ext{ atm}$$

Question 3

Which statement about the relationship between temperature and volume for a gas at constant pressure is correct?

Accepted Answer

As temperature increases, volume increases proportionally.

Question 4

A balloon has a volume of 2.80 L at 298 K. If the temperature is lowered to 273 K at constant pressure, what is the new volume?

Accepted Answer

$$\frac{V_1$}{T_1$} = \frac{V_2$}{T_2$}$$; $$V_2$$ = \frac{V_1T_2}{$$T_1$$} = \frac{2.80 	ext{ L} 	imes 273 	ext{ K}}{298 	ext{ K}} = 2.56 	ext{ L}$$

Question 5

Which of the following is the correct form of the ideal gas law?

Accepted Answer

$$PV = nRT$$

Question 6

At STP, what is the volume occupied by 2 moles of an ideal gas?

Accepted Answer

$$2 	ext{ mol} 	imes 22.4 	ext{ L/mol} = 44.8 	ext{ L}$$

Question 7

A gas sample contains 0.552 mol at 305 K in a 12.0 L container. What is the pressure in atm?

Accepted Answer

$$P = \frac{nRT}{V} = \frac{0.552 	imes 0.08206 	imes 305}{12.0} = 1.15 	ext{ atm}$$

Question 8

Which of the following factors will NOT increase the pressure of a gas in a sealed container?

Accepted Answer

Decreasing the speed of the gas particles.

Question 9

A scuba tank contains a mixture of 24.2 g He and 4.32 g O$$_2. $$The total pressure is 12.099 atm. What is the partial pressure of He? (He: 4.00 g/mol, O$$_2$$: 32.00 g/mol)

Accepted Answer

First, calculate moles: $$n_{He} = \frac{24.2}{4.00} = 6.05$$ mol, $$n_{O_2$} = \frac{4.32}{32.00} = 0.135$$ mol. Total moles $$= 6.05 + 0.135 = 6.185$$ mol. Mole fraction $$X_{He} = \frac{6.05}{6.185} = 0.978$$; Partial pressure $$P_{He} = X_{He} 	imes P_{total} = 0.978 	imes 12.099 = 11.84$$ atm.

Question 10

Which of the following correctly describes the relationship between the density of a gas and its molar mass at STP?

Accepted Answer

Density is directly proportional to molar mass.

Question 11

A cylinder contains 0.120 mol of gas in 2.80 L. After a reaction, 0.621 mol of gas is present. What is the final volume, assuming constant temperature and pressure?

Accepted Answer

$$\frac{V_1$}{n_1$} = \frac{V_2$}{n_2$}$$; $$V_2$$ = \frac{n_2V_1}{$$n_1$$} = \frac{0.621 	imes 2.80}{0.120} = 14.5 	ext{ L}$$

Question 12

Which equation can be used to calculate the density of a gas under non-STP conditions?

Accepted Answer

$$d = \frac{PM}{RT}$$

Question 13

A light bulb contains 2.00 g Ne and 0.350 g Hg. The total pressure is 2.75 torr. What is the partial pressure of Ne? (Ne: 20.18 g/mol, Hg: 200.59 g/mol)

Accepted Answer

Moles Ne: $$\frac{2.00}{20.18} = 0.099$$ mol; Moles Hg: $$\frac{0.350}{200.59} = 0.00175$$ mol; Total moles $$= 0.099 + 0.00175 = 0.10075$$ mol; $$X_{Ne} = \frac{0.099}{0.10075} = 0.983$$; $$P_{Ne} = 0.983 	imes 2.75 = 2.70$$ torr.

Question 14

Which of the following is NOT a valid unit for measuring gas pressure?

Accepted Answer

Joule (J)

Question 15

If the volume of a gas is doubled at constant temperature, what happens to the pressure?

Accepted Answer

It is halved.

Question 16

Which of the following best describes the concept of partial pressure in a mixture of gases?

Accepted Answer

The pressure exerted by each individual gas as if it were alone in the container.

Question 17

A gas has a density of 1.25 g/L at STP. What is its molar mass?

Accepted Answer

$$M = d 	imes 22.4 = 1.25 	ext{ g/L} 	imes 22.4 	ext{ L} = 28.0 	ext{ g/mol}$$

Question 18

Which of the following statements about the behavior of ideal gases is correct?

Accepted Answer

Ideal gases do not interact and behave independently of each other.

Gases – Properties and Behavior

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