Q: A 2.00 L sample of nitrogen gas at 1.00 atm and 273 K is compressed to 1.00 L at constant temperature. What is the final pressure of the gas?

$$P_2$$ = \frac{$$P_1$$ $$V_1$$}{$$V_2$$} = \frac{1.00 \ \text{atm} \times 2.00 \ \text{L}}{1.00 \ \text{L}} = 2.00 \ \text{atm}$$

Q: A 250.0 mL sample of CO gas at 1.20 atm is compressed to 125.0 mL at constant temperature. What is the new pressure?

$$P_2$$ = \frac{$$P_1$$ $$V_1$$}{$$V_2$$} = \frac{1.20 \ \text{atm} \times 250.0 \ \text{mL}}{125.0 \ \text{mL}} = 2.40 \ \text{atm}$$

Q: A 15.5 g sample of an unknown gas occupies 5.75 L at 25°C and 1.08 atm. What is the molar mass of the gas?

$$M = \frac{mRT}{PV} = \frac{15.5 \ \text{g} \times 0.0821 \ \text{L-atm/mol-K} \times 298 \ \text{K}}{1.08 \ \text{atm} \times 5.75 \ \text{L}} = 64.7 \ \text{g/mol}$$

Q: A mixture of gases contains 2.0 mol $$N_2$$, 1.0 mol $$O_2$$, and 1.0 mol $$Ar at a $$total pressure of 800 mmHg. What is the partial pressure of $$O_2$$?

$$P_{O_2$} = X_{O_2$} \times P_{total} = \frac{1.0}{4.0} \times 800 \ \text{mmHg} = 200 \ \text{mmHg}$$

Q: A sample of hydrogen gas is collected over water at 19°C and a total pressure of 739 mmHg. The vapor pressure of water at 19°C is 17 mmHg. What is the partial pressure of hydrogen gas?

$$P_{H_2$} = P_{total} - P_{H_2O} = 739 \ \text{mmHg} - 17 \ \text{mmHg} = 722 \ \text{mmHg}$$

Question 1

Which of the following statements best explains why gases have much lower densities than solids and liquids?

Accepted Answer

Gas molecules are far apart compared to solids and liquids, resulting in much lower mass per unit volume.

Question 2

A 2.00 L sample of nitrogen gas at 1.00 atm and 273 K is compressed to 1.00 L at constant temperature. What is the final pressure of the gas?

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$}{$$V_2$$} = \frac{1.00 \ 	ext{atm} 	imes 2.00 \ 	ext{L}}{1.00 \ 	ext{L}} = 2.00 \ 	ext{atm}$$

Question 3

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

Accepted Answer

Pressure is directly proportional to temperature (in Kelvin).

Question 4

A 250.0 mL sample of CO gas at 1.20 atm is compressed to 125.0 mL at constant temperature. What is the new pressure?

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$}{$$V_2$$} = \frac{1.20 \ 	ext{atm} 	imes 250.0 \ 	ext{mL}}{125.0 \ 	ext{mL}} = 2.40 \ 	ext{atm}$$

Question 5

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

Accepted Answer

Gas molecules occupy a significant volume compared to the container.

Question 6

A 15.5 g sample of an unknown gas occupies 5.75 L at 25°C and 1.08 atm. What is the molar mass of the gas?

Accepted Answer

$$M = \frac{mRT}{PV} = \frac{15.5 \ 	ext{g} 	imes 0.0821 \ 	ext{L-atm/mol-K} 	imes 298 \ 	ext{K}}{1.08 \ 	ext{atm} 	imes 5.75 \ 	ext{L}} = 64.7 \ 	ext{g/mol}$$

Question 7

Which of the following gases will have the highest root-mean-square (rms) speed at 25°C?

Accepted Answer

Hydrogen, $$H_2$$

Question 8

A mixture of gases contains 2.0 mol $$N_2$$, 1.0 mol $$O_2$$, and 1.0 mol $$Ar at a $$total pressure of 800 mmHg. What is the partial pressure of $$O_2$$?

Accepted Answer

$$P_{O_2$} = X_{O_2$} 	imes P_{total} = \frac{1.0}{4.0} 	imes 800 \ 	ext{mmHg} = 200 \ 	ext{mmHg}$$

Question 9

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.

Question 10

A sample of hydrogen gas is collected over water at 19°C and a total pressure of 739 mmHg. The vapor pressure of water at 19°C is 17 mmHg. What is the partial pressure of hydrogen gas?

Accepted Answer

$$P_{H_2$} = P_{total} - P_{H_2O} = 739 \ 	ext{mmHg} - 17 \ 	ext{mmHg} = 722 \ 	ext{mmHg}$$

Question 11

Which of the following gases would deviate most from ideal behavior under high pressure and low temperature?

Accepted Answer

Ammonia, $$NH_3$$

Question 12

A 5.00 L sample of neon at 25°C and 0.975 atm is heated to 325 K. If the new volume is 10.0 L, what is the new pressure?

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$T_1$$ $$V_2$$} = \frac{0.975 	imes 5.00 	imes 325}{298 	imes 10.0} = 0.532 \ 	ext{atm}$$

Question 13

Which of the following is the correct value for the molar volume of an ideal gas at STP?

Accepted Answer

$$22.4 \ 	ext{L/mol}$$

Question 14

A sample of $$C_2H_2 ($$acetylene) gas at STP has a density of 1.17 g/L. What is the molar mass of $$C_2H_2$$?

Accepted Answer

$$M = D 	imes 22.4 = 1.17 \ 	ext{g/L} 	imes 22.4 \ 	ext{L/mol} = 26.2 \ 	ext{g/mol}$$

Question 15

Which of the following best explains why the pressure of a real gas is lower than predicted by the ideal gas law at moderate pressures?

Accepted Answer

Attractive forces between molecules reduce the frequency and force of collisions with the container walls.

Question 16

A 1.00 L sample of $$O_2 at $$STP contains how many molecules?

Accepted Answer

$$\frac{1.00}{22.4} 	imes 6.02 	imes 10$$^{23}$$ = 2.69 	imes 10$$^{22}$$ molecules

Question 17

Which of the following best describes diffusion?

Accepted Answer

The process by which a gas spreads through another gas to occupy the available space uniformly.

Question 18

If a gas sample is heated from 225 K to 675 K at constant pressure, and its initial volume is 25.0 mL, what is the final volume?

Accepted Answer

$$V_2$$ = $$V_1$$ \frac{$$T_2$$}{$$T_1$$} = 25.0 \ 	ext{mL} 	imes \frac{675}{225} = 75.0 \ 	ext{mL}$$

Gases: Properties, Pressure, and Conversions (General Chemistry Study Notes)

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