Q: A sample of gas occupies 2.0 L at 1.0 atm. If the pressure is increased to 2.0 atm at constant temperature, what will be the new volume of the gas?

$$V_2$$ = \frac{$$P_1$$ $$V_1$$}{$$P_2$$} = \frac{1.0 \times 2.0}{2.0} = 1.0\ \mathrm{L}$$

Q: A gas sample has a mass of 4.00 g and occupies 2.00 L at 1.00 atm and 273.15 K. What is the molar mass of the gas?

$$M = \frac{mRT}{PV} = \frac{4.00 \times 0.0821 \times 273.15}{1.00 \times 2.00} = 45.0\ \mathrm{g/mol}$$

Q: A mixture of gases is collected over water at 25°C. The total pressure is 760 Torr and the vapor pressure of water at 25°C is 24 Torr. What is the partial pressure of the dry gas?

$$P_{\text{dry gas}} = 760\ \text{Torr} - 24\ \text{Torr} = 736\ \text{Torr}$$

Q: Which of the following correctly expresses Dalton’s law of partial pressures?

$$P_{\text{total}} = P_1$ + P_2$ + P_3$ + \ldots$$

Q: A 5.00 L container holds 0.50 mol of a gas at 300 K. What is the pressure in atm? (Use $$R = 0.0821\ \mathrm{L\ atm\ $$mol^{-1}$$\ K$$^{-1}$$})$$

$$P = \frac{nRT}{V} = \frac{0.50 \times 0.0821 \times 300}{5.00} = 2.46\ \mathrm{atm}$$

Question 1

Which of the following best describes the molecular origin of pressure in a gas?

Accepted Answer

Pressure results from the collisions of gas molecules with the walls of the container.

Question 2

A sample of gas occupies 2.0 L at 1.0 atm. If the pressure is increased to 2.0 atm at constant temperature, what will be the new volume of the gas?

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$}{$$P_2$$} = \frac{1.0 	imes 2.0}{2.0} = 1.0\ \mathrm{L}$$

Question 3

Which of the following is the correct SI unit for pressure?

Accepted Answer

Pa

Question 4

According to Charles's Law, what happens to the volume of a gas if the temperature is doubled at constant pressure?

Accepted Answer

The volume doubles.

Question 5

A 1.00 mol sample of an ideal gas is at STP (1 bar, 273.15 K). What is its molar volume?

Accepted Answer

$$22.7\ \mathrm{L}$$

Question 6

Which equation correctly expresses the ideal gas law?

Accepted Answer

$$PV = nRT$$

Question 7

A mixture contains 2.0 mol O$$_2$$, 1.0 mol N$$_2$$, and 1.0 mol CO$$_2 in a 10.0 L $$container at 300 K. What is the mole fraction of O$$_2$$?

Accepted Answer

$$x_{O_2$} = \frac{2.0}{2.0 + 1.0 + 1.0} = 0.5$$

Question 8

Which statement about the kinetic molecular theory of gases is correct?

Accepted Answer

Gas molecules undergo elastic collisions with each other and the container walls.

Question 9

A gas sample has a mass of 4.00 g and occupies 2.00 L at 1.00 atm and 273.15 K. What is the molar mass of the gas?

Accepted Answer

$$M = \frac{mRT}{PV} = \frac{4.00 	imes 0.0821 	imes 273.15}{1.00 	imes 2.00} = 45.0\ \mathrm{g/mol}$$

Question 10

Which of the following is a limitation of the ideal gas law?

Accepted Answer

It does not account for the finite volume of gas molecules at high pressure.

Question 11

A mixture of gases is collected over water at 25°C. The total pressure is 760 Torr and the vapor pressure of water at 25°C is 24 Torr. What is the partial pressure of the dry gas?

Accepted Answer

$$P_{	ext{dry gas}} = 760\ 	ext{Torr} - 24\ 	ext{Torr} = 736\ 	ext{Torr}$$

Question 12

Which of the following correctly expresses Dalton’s law of partial pressures?

Accepted Answer

$$P_{	ext{total}} = P_1$ + P_2$ + P_3$ + \ldots$$

Question 13

Which of the following statements about the average kinetic energy of gas molecules is true?

Accepted Answer

It depends only on the temperature, not on the identity of the gas.

Question 14

A 5.00 L container holds 0.50 mol of a gas at 300 K. What is the pressure in atm? (Use $$R = 0.0821\ \mathrm{L\ atm\ $$mol^{-1}$$\ K$$^{-1}$$})$$

Accepted Answer

$$P = \frac{nRT}{V} = \frac{0.50 	imes 0.0821 	imes 300}{5.00} = 2.46\ \mathrm{atm}$$

Question 15

Which of the following is a correction made by the van der Waals equation for real gases?

Accepted Answer

It accounts for the finite volume of gas molecules and intermolecular forces.

Question 16

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

Accepted Answer

The pressure increases.

Question 17

A chemical reaction produces 0.50 mol of H$$_2$$ gas at STP. What volume will the gas occupy?

Accepted Answer

$$V = n 	imes 22.7\ \mathrm{L} = 0.50 	imes 22.7 = 11.35\ \mathrm{L}$$

Question 18

Which of the following gases will have the highest average molecular speed at the same temperature?

Accepted Answer

Hydrogen ($$H_2)$$

Question 19

Which formula gives the average kinetic energy per mole of a gas?

Accepted Answer

$$KE_{avg} = \frac{3}{2} RT$$

Study Notes: Gases (General Chemistry, Chapter 5)

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