Q: A sample of gas occupies 4.0 L at 2.0 atm. If the pressure is increased to 8.0 atm at constant temperature, what will be the new volume of the gas?

$$V_2$$ = \frac{P_1V_1}{$$P_2$$} = \frac{(2.0\ \text{atm})(4.0\ \text{L})}{8.0\ \text{atm}} = 1.0\ \text{L}$$

Q: A 2.0 L sample of gas at 300 K and 1.0 atm is compressed to 1.0 L and heated to 600 K. What is the final pressure?

$$P_2$$ = \frac{P_1V_1T_2}{T_1V_2} = \frac{(1.0\ \text{atm})(2.0\ \text{L})(600\ \text{K})}{(300\ \text{K})(1.0\ \text{L})} = 4.0\ \text{atm}$$

Q: A 5.0 L sample of oxygen gas at 27$$^\circC $$and 2.0 atm contains how many moles of O$$_2$$? ($$R = 0.0821\ \text{L} \cdot \text{atm} / \text{mol} \cdot \text{K})$$

$$n = \frac{PV}{RT} = \frac{(2.0\ \text{atm})(5.0\ \text{L})}{0.0821\ \text{L} \cdot \text{atm} / \text{mol} \cdot \text{K} \times 300\ \text{K}} = 0.41\ \text{mol}$$

Q: A room measures 3.0 m × 4.0 m × 2.5 m. How many moles of air does it contain at STP? (1 mol gas at STP = 22.4 L)

Volume = $$3.0 \times 4.0 \times 2.5 = 30.0\ \text{m}^3 = 30,000\ \text{L}$$; $$n = \frac{30,000\ \text{L}}{22.4\ \text{L/mol}} = 1,340\ \text{mol}$$

Q: A mixture of gases contains 30% oxygen, 60% nitrogen, and 10% carbon dioxide by volume. If the total pressure is 1.0 atm, what is the partial pressure of nitrogen?

$$P_{N_2$} = 0.60 \times 1.0\ \text{atm} = 0.60\ \text{atm}$$

Question 1

Which of the following phase changes is exothermic and results in a decrease in entropy ($$\Delta S$$)?

Accepted Answer

Condensation of water vapor

Question 2

A sample of gas occupies 4.0 L at 2.0 atm. If the pressure is increased to 8.0 atm at constant temperature, what will be the new volume of the gas?

Accepted Answer

$$V_2$$ = \frac{P_1V_1}{$$P_2$$} = \frac{(2.0\ 	ext{atm})(4.0\ 	ext{L})}{8.0\ 	ext{atm}} = 1.0\ 	ext{L}$$

Question 3

Which of the following substances would you expect to have the highest boiling point, and why?

Accepted Answer

Acetic acid, CH$$_3$$COOH, because it has hydrogen bonding in addition to dipole-dipole and London dispersion forces

Question 4

A 2.0 L sample of gas at 300 K and 1.0 atm is compressed to 1.0 L and heated to 600 K. What is the final pressure?

Accepted Answer

$$P_2$$ = \frac{P_1V_1T_2}{T_1V_2} = \frac{(1.0\ 	ext{atm})(2.0\ 	ext{L})(600\ 	ext{K})}{(300\ 	ext{K})(1.0\ 	ext{L})} = 4.0\ 	ext{atm}$$

Question 5

Which of the following best explains why water has a much higher boiling point than hydrogen sulfide (H$$_2S$$)?

Accepted Answer

Water forms hydrogen bonds, which are much stronger than the dipole-dipole forces in H$$_2S$$

Question 6

A 5.0 L sample of oxygen gas at 27$$^\circC $$and 2.0 atm contains how many moles of O$$_2$$? ($$R = 0.0821\ 	ext{L} \cdot 	ext{atm} / 	ext{mol} \cdot 	ext{K})$$

Accepted Answer

$$n = \frac{PV}{RT} = \frac{(2.0\ 	ext{atm})(5.0\ 	ext{L})}{0.0821\ 	ext{L} \cdot 	ext{atm} / 	ext{mol} \cdot 	ext{K} 	imes 300\ 	ext{K}} = 0.41\ 	ext{mol}$$

Question 7

Which of the following statements about crystalline and amorphous solids is correct?

Accepted Answer

Crystalline solids have a regular, repeating arrangement of particles, while amorphous solids do not

Question 8

A room measures 3.0 m × 4.0 m × 2.5 m. How many moles of air does it contain at STP? (1 mol gas at STP = 22.4 L)

Accepted Answer

Volume = $$3.0 	imes 4.0 	imes 2.5 = 30.0\ 	ext{m}^3 = 30,000\ 	ext{L}$$; $$n = \frac{30,000\ 	ext{L}}{22.4\ 	ext{L/mol}} = 1,340\ 	ext{mol}$$

Question 9

Which of the following best describes the relationship between vapor pressure and boiling point for a liquid?

Accepted Answer

A liquid boils when its vapor pressure equals atmospheric pressure

Question 10

A mixture of gases contains 30% oxygen, 60% nitrogen, and 10% carbon dioxide by volume. If the total pressure is 1.0 atm, what is the partial pressure of nitrogen?

Accepted Answer

$$P_{N_2$} = 0.60 	imes 1.0\ 	ext{atm} = 0.60\ 	ext{atm}$$

Question 11

Which of the following is NOT a postulate of the kinetic-molecular theory of gases?

Accepted Answer

Gas particles occupy a significant fraction of the total volume

Question 12

Which of the following liquids would you expect to have the highest viscosity?

Accepted Answer

A liquid with strong hydrogen bonding

Question 13

A 1.0 L sample of gas at 300 K contains 0.040 mol. If the amount of gas is doubled at constant temperature and pressure, what will be the new volume?

Accepted Answer

$$V_2$$ = $$V_1$$ 	imes \frac{$$n_2$$}{$$n_1$$} = 1.0\ 	ext{L} 	imes \frac{0.080}{0.040} = 2.0\ 	ext{L}$$

Question 14

Which of the following best explains why metals are malleable and conduct electricity?

Accepted Answer

Metals have a sea of delocalized electrons that can move freely

Question 15

How much heat (in J) is required to melt 10.0 g of naphthalene (heat of fusion = 149 J/g)?

Accepted Answer

$$q = m 	imes \Delta H_{fus} = (10.0\ 	ext{g})(149\ 	ext{J/g}) = 1,490\ 	ext{J}$$

Question 16

Which of the following statements about intermolecular forces is correct?

Accepted Answer

London dispersion forces are present in all molecules

States of Matter, Intermolecular Forces, and Gas Laws: Core Concepts in General Chemistry

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