Q: A 250 mL flask contains CO2 gas at 1.3 atm and 31°C. How many moles of CO2 are present? (Use $$R = 0.08206 L-$$atm/mol-K)

$$n = \frac{PV}{RT} = \frac{(1.3)(0.250)}{0.08206 \times 304} = 0.0134$$ mol

Q: Convert 147.2 kPa to torr.

$$147.2 \text{ kPa} \times \frac{760 \text{ torr}}{101.325 \text{ kPa}} = 1104 \text{ torr}$$

Q: What is the density of carbon tetrachloride vapor at 714 torr and 125°C? (Molar mass = 153.82 g/mol, $$R = 0.08206 L-$$atm/mol-K)

$$d = \frac{PM}{RT} = \frac{(0.939)(153.82)}{0.08206 \times 398} = 4.41 g/L$$

Q: A container holds a mixture of gases: 2 mol O2, 3 mol N2, and 1 mol CO2. If the total pressure is 800 torr, what is the partial pressure of N2?

$$P_{N_2$} = X_{N_2$} P_t = \frac{3}{6} \times 800 = 400$$ torr

Question 1

Which of the following statements best explains why gases are compressible, according to the kinetic-molecular theory?

Accepted Answer

The combined volume of all gas molecules is negligible compared to the total volume of the container.

Question 2

A 250 mL flask contains CO2 gas at 1.3 atm and 31°C. How many moles of CO2 are present? (Use $$R = 0.08206 L-$$atm/mol-K)

Accepted Answer

$$n = \frac{PV}{RT} = \frac{(1.3)(0.250)}{0.08206 	imes 304} = 0.0134$$ mol

Question 3

Which gas listed in Table 10.1 is both colorless and odorless, but highly toxic?

Accepted Answer

Carbon monoxide (CO)

Question 4

A balloon filled with helium rises through the atmosphere. What happens to the volume of the balloon as it ascends, assuming the temperature decreases and the pressure decreases?

Accepted Answer

The volume increases due to lower pressure, but may decrease due to lower temperature.

Question 5

Convert 147.2 kPa to torr.

Accepted Answer

$$147.2 	ext{ kPa} 	imes \frac{760 	ext{ torr}}{101.325 	ext{ kPa}} = 1104 	ext{ torr}$$

Question 6

Which equation describes the relationship between the rate of effusion of two gases and their molar masses?

Accepted Answer

$$\frac{r_1$}{r_2$} = \sqrt{\frac{M_2$}{M_1$}}$$

Question 7

A mixture of 6.00 g O2 and 9.00 g CH4 is placed in a 15.0-L vessel at 0°C. What is the total pressure in the vessel? (Use $$R = 0.08206 L-$$atm/mol-K)

Accepted Answer

$$P_t = \frac{n_{O_2$} + n_{CH_4$}}{V}RT = 0.82$$ atm

Question 8

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

Accepted Answer

Gas molecules exert attractive and repulsive forces on each other.

Question 9

What is the density of carbon tetrachloride vapor at 714 torr and 125°C? (Molar mass = 153.82 g/mol, $$R = 0.08206 L-$$atm/mol-K)

Accepted Answer

$$d = \frac{PM}{RT} = \frac{(0.939)(153.82)}{0.08206 	imes 398} = 4.41 g/L$$

Question 10

A gas sample is heated from 25°C to 450°C in a sealed aerosol can. If the initial pressure is 1.5 atm, what is the final pressure? (Assume constant volume)

Accepted Answer

$$P_2$$ = $$P_1$$ \frac{$$T_2$$}{$$T_1$$} = 1.5 \frac{723}{298} = 3.63$$ atm

Question 11

Which gas will effuse fastest through a porous membrane: He, N2, or CH4?

Accepted Answer

He

Question 12

A container holds a mixture of gases: 2 mol O2, 3 mol N2, and 1 mol CO2. If the total pressure is 800 torr, what is the partial pressure of N2?

Accepted Answer

$$P_{N_2$} = X_{N_2$} P_t = \frac{3}{6} 	imes 800 = 400$$ torr

Question 13

Which of the following best describes the relationship between volume and pressure for a fixed amount of gas at constant temperature?

Accepted Answer

Volume is inversely proportional to pressure.

Question 14

Calculate the root-mean-square speed ($$u_{rms}) of O2 $$molecules at 25°C. (Molar mass O2 = 32.0 g/mol, $$R = 8.314 J/$$mol-K)

Accepted Answer

$$u_{rms} = \sqrt{\frac{3RT}{M}} = \sqrt{\frac{3 	imes 8.314 	imes 298}{0.032}} = 461 m/s$$

Question 15

If 2.5 L of N2 reacts with 3.5 L of H2 at STP, how many liters of NH3 are produced?

Accepted Answer

1.67 L NH3

Question 16

Which of the following is a real-life example of gas diffusion?

Accepted Answer

Perfume molecules spreading throughout a room.

Question 17

Which unit is NOT equivalent to 1 atm?

Accepted Answer

62.36 L-torr/mol-K

Question 18

A gas mixture contains 18% O2 by mole fraction. If the total pressure is 745 torr, what is the partial pressure of O2?

Accepted Answer

$$P_{O_2$} = X_{O_2$} P_t = 0.18 	imes 745 = 134$$ torr

Chapter 10: Gases – Properties, Laws, and Applications

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