Q: A 0.300 mol sample of naphthalene (molar mass = 128 g/mol) requires 19.0 kJ/mol to melt. How much heat is required to melt the sample?

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

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)

First, calculate the volume: $$V = 4.11 \times 5.36 \times 2.58 = 56.8\ \mathrm{m^3$} = 56,800\ \mathrm{L}$$; $$n = \frac{56,800}{22.4} = 2,536\ \mathrm{mol}$$

Question 1

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

Accepted Answer

Freezing of liquid water to ice

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 dipole-dipole interactions

Question 4

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

Accepted Answer

$$n = \frac{5540\ \mathrm{g}}{16.0\ \mathrm{g/mol}} = 346.25\ \mathrm{mol}$$; $$T = 293.15\ \mathrm{K}$$; $$P = \frac{nRT}{V} = \frac{346.25 	imes 0.0821 	imes 293.15}{43.8} = 190.5\ \mathrm{atm}$$

Question 5

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

Accepted Answer

Gas particles exert attractive forces on each other.

Question 6

A 0.300 mol sample of naphthalene (molar mass = 128 g/mol) requires 19.0 kJ/mol to melt. How much heat is required to melt the sample?

Accepted Answer

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

Question 7

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

Accepted Answer

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

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 is needed to maintain this pressure?

Accepted Answer

$$T_2$$ = \frac{$$P_2$$ $$V_2$$ $$T_1$$}{$$P_1$$ $$V_1$$} = \frac{2.8 	imes 2.0 	imes 300}{1.2 	imes 6.3} = 223.8\ \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

First, calculate the volume: $$V = 4.11 	imes 5.36 	imes 2.58 = 56.8\ \mathrm{m^3$} = 56,800\ \mathrm{L}$$; $$n = \frac{56,800}{22.4} = 2,536\ \mathrm{mol}$$

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 describes an amorphous solid?

Accepted Answer

It has randomly arranged particles with no long-range order.

Question 14

A sample of gas at 1.0 atm and 300 K occupies 500 mL. What will the pressure be if the temperature is increased to 600 K and the volume is decreased to 250 mL?

Accepted Answer

$$P_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$T_1$$ $$V_2$$} = \frac{1.0 	imes 500 	imes 600}{300 	imes 250} = 4.0\ \mathrm{atm}$$

Question 15

Which of the following best explains why ionic solids have high melting points?

Accepted Answer

They are composed of ions held together by strong electrostatic forces.

Question 16

A balloon filled with 2.0 L of air at 25 $$^\circC is $$placed in a freezer at -25 $$^\circC. $$What is the new volume of the balloon, assuming constant pressure?

Accepted Answer

$$V_2$$ = $$V_1$$ \frac{$$T_2$$}{$$T_1$$} = 2.0 	imes \frac{248}{298} = 1.67\ \mathrm{L}$$

Question 17

Which of the following is NOT a property of liquids that is influenced by intermolecular forces?

Accepted Answer

Molar mass

Question 18

A typical bicycle tire is inflated to 55 psi. What is this pressure in atmospheres? (1 atm = 14.7 psi)

Accepted Answer

$$P = \frac{55}{14.7} = 3.74\ \mathrm{atm}$$

Gases, Liquids, and Solids: Study Guide for GOB Chemistry

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