Q: A 0.300 mol sample of naphthalene (molar mass = 128 g/mol, heat of fusion = 19.0 kJ/mol) is to be melted. How much heat is required?

$$q = n \times \Delta H_{fus} = (0.300\ \mathrm{mol})(19.0\ \mathrm{kJ/mol}) = 5.7\ \mathrm{kJ}$$

Q: A room measures 4.11 m wide, 5.36 m long, and 2.58 m high. How many moles of air are present at STP? (1 mol gas at STP = 22.4 L)

Volume = $$4.11 \times 5.36 \times 2.58 = 56.8\ \mathrm{m}^3 = 56,800\ \mathrm{L}$$; $$n = \frac{56,800}{22.4} = 2,540\ \mathrm{mol}$$

Question 1

Which of the following phase changes is exothermic and results in a decrease in entropy?

Accepted Answer

Condensation of water vapor to liquid water

Question 2

A sample of gas occupies 2.50 L at 1.00 atm and 300 K. If the pressure is increased to 2.00 atm and the temperature is raised to 400 K, what is the new volume of the gas? (Assume the amount of gas is constant.)

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$T_1$$ $$P_2$$} = \frac{(1.00)(2.50)(400)}{(300)(2.00)} = 1.67\ \mathrm{L}$$

Question 3

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

Accepted Answer

Acetic acid ($$\mathrm{CH_3COOH}$$), because it can form hydrogen bonds and has higher molecular weight

Question 4

A steel cylinder contains 5.54 kg of methane ($$\mathrm{CH_4$}$$, molar mass = 16.0 g/mol) in a 43.8 L container at 20.0 $$^\circC. $$What is the pressure inside the cylinder in atmospheres? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$n = \frac{5540\ \mathrm{g}}{16.0\ \mathrm{g/mol}} = 346.25\ \mathrm{mol}$$; $$T = 293.15\ \mathrm{K}$$; $$P = \frac{nRT}{V} = \frac{(346.25)(0.0821)(293.15)}{43.8} = 190\ \mathrm{atm}$$

Question 5

Which of the following best explains why water has a much higher boiling point than methane ($$\mathrm{CH_4$}$$)?

Accepted Answer

Water forms hydrogen bonds, which are much stronger than the London dispersion forces present in methane.

Question 6

A 0.300 mol sample of naphthalene (molar mass = 128 g/mol, heat of fusion = 19.0 kJ/mol) is to be melted. How much heat is required?

Accepted Answer

$$q = n 	imes \Delta H_{fus} = (0.300\ \mathrm{mol})(19.0\ \mathrm{kJ/mol}) = 5.7\ \mathrm{kJ}$$

Question 7

Which of the following statements about the kinetic-molecular theory of gases is FALSE?

Accepted Answer

Gas particles experience strong attractive forces with each other.

Question 8

A 6.3 L sample of helium gas at 1.2 atm and 300 K is transferred to a 2.0 L tank and maintained at a pressure of 2.8 atm. What temperature (in K) is needed to maintain this pressure?

Accepted Answer

$$T_2$$ = \frac{$$P_2$$ $$V_2$$ $$T_1$$}{$$P_1$$ $$V_1$$} = \frac{(2.8)(2.0)(300)}{(1.2)(6.3)} = 223\ \mathrm{K}$$

Question 9

Which of the following best describes the structure and properties of metallic solids?

Accepted Answer

They are arrays of metal cations in a sea of delocalized electrons, making them malleable and good conductors.

Question 10

A room measures 4.11 m wide, 5.36 m long, and 2.58 m high. How many moles of air are present at STP? (1 mol gas at STP = 22.4 L)

Accepted Answer

Volume = $$4.11 	imes 5.36 	imes 2.58 = 56.8\ \mathrm{m}^3 = 56,800\ \mathrm{L}$$; $$n = \frac{56,800}{22.4} = 2,540\ \mathrm{mol}$$

Question 11

Which of the following statements about vapor pressure is correct?

Accepted Answer

Vapor pressure is the partial pressure of vapor molecules in equilibrium with a liquid.

Question 12

A closed flask contains a mixture of gases: 70% nitrogen, 20% oxygen, and 10% argon by volume. If the total pressure is 800 mmHg, what is the partial pressure of oxygen?

Accepted Answer

$$P_{O_2$} = 0.20 	imes 800 = 160\ \mathrm{mmHg}$$

Question 13

Which of the following best explains why ionic solids, such as sodium chloride, have high melting points?

Accepted Answer

They are held together by strong electrostatic attractions between oppositely charged ions.

Question 14

A sample of gas at 1.00 atm and 273 K occupies 22.4 L. If the temperature is increased to 546 K at constant pressure, what is the new volume?

Accepted Answer

$$V_2$$ = $$V_1$$ \frac{$$T_2$$}{$$T_1$$} = 22.4 	imes \frac{546}{273} = 44.8\ \mathrm{L}$$

Question 15

Which of the following is a property of amorphous solids?

Accepted Answer

They soften over a wide temperature range and break with curved surfaces.

Question 16

Which of the following best describes the relationship between viscosity and intermolecular forces in liquids?

Accepted Answer

Viscosity increases as intermolecular forces increase.

Question 17

A balloon filled with 2.00 mol of helium at 1.00 atm and 273 K has a volume of 44.8 L. If the amount of helium is doubled at constant temperature and pressure, what will be the new volume?

Accepted Answer

$$V_2$$ = $$V_1$$ \frac{$$n_2$$}{$$n_1$$} = 44.8 	imes \frac{4.00}{2.00} = 89.6\ \mathrm{L}$$

Question 18

Which of the following is NOT a type of intermolecular force?

Accepted Answer

Ionic bonding

Gases, Liquids, and Solids: States of Matter, Intermolecular Forces, and Gas Laws

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