284 AP Chemistry

4. Which of the following pairs areinversely proportional to eachother, assuming all other .conditions are kept constant?

Practice Exercises

Multiple-ChoiceFor the first five problems below, one or more of the following responses will app_each response may be used more than once or not at all in these questions.

I. increased volumeII. increased temperatureIII. increased average kinetic

energyIV increased effusion rateV increased pressure

1. Considering Boyle's law, a gas willhave an if thepressure is reduced.

(A) I(B) II(C) III(D) IV(E) II and III

2. There will be an _if methane, CH4, rather thanethane, CH3CH3 isthe gas usedunder comparable conditions.

(A) I and III(B) II(C) III and V(D) IV(E) V

3. The kinetic molecular theorypostulates a direct relationshipbetween

(A) I and III(B) II and III(C) III and V(D) IV(E) V

(A) I, V(B) II, III(C) III, V(D) IV, II(E) v, II

5. A gas will behave more like anideal gas if we have an ---,;and an ------(A) I, II(B) II, III(C) III, V(D) IV, V(E) V, II

6. What volume will 2.50 mol ofKoccupy at 45°C and 1.50 atm 0 -pressure?

(A) 43.5 L(B) 6.08 L(C) 0.0233 L(D) 56.00 L(E) 14.9 L

7. How many moles of helium areneeded to fill a balloon that has c.volume of 6.45 L and a pressure800 mm Hg at a room temperaof 24°C? Assume ideal gasbehavior.

(A) 0.288(B) 214(C) 0.278(D) 2.65 X 103

(E) 0.255

8. If ideal gas behavior is assumed,what is the density of neon atSTP?(A) 1.11 g L-](B) 448 g L-j

(C) 0.009 g L-](D) 0.901 g L-1(E) 1.25 g L-]

9. A sample of CO has a pressure of58 mm Hg and a volume of155 mL. When the CO isquantitatively transferred to a1.00-L flask, the pressure of thegas will be

(A) 374 mm Hg(B) 8990 mm Hg(C) 111 mm Hg(D) 8.99 mm Hg(E) 2.67 mm Hg

10. At 30°C a sample of hydrogen iscollected over water [PH,o=31.82 mm Hg at 30°C] in a500-mL flask. The total pressurein the collection flask is745 mm Hg. What will be thepercent of error in the amount ofhydrogen reported if thecorrection for the vapor pressureof water is not made?

(A) 0.0%(B) +4.5%(C) -4.5%(D) +4.3%(E) -4.3%

11. What will the total pressure be ina 2.50-L flask at 25°C if itcontains 0.016 mol of CO2 and0.035 mol of CHi

(A) 31.4 mm Hg(B) 380 mm Hg(C) 0.041 mm Hg(D) 935 mm Hg(E) 1.23 atm

12. The carbon dioxide from thecombustion of 1.50 g of C2H6 iscollected over water at 25°C. Thepressure of CO2 in the collectionflask is 746 mm Hg, and thevolume is 2.00 L. How much ofthe CO2 formed apparentlydissolved in the water of thepneumatic trough?

(A) 0.0814 mol(B) 0.87 g(C) 1.79 g(D) 0.100 mol(E) 2.55 g

13. In which of the following is itimpossible to predict whether thepressure of a gas will increase,decrease, or stay the same?

(A) A gas sample is heated.(B) A gas sample is heated, andthe volume is increased.

(C) A gas sample is cooled, andsome gas is withdrawn.

(D) Additional gas is added to asample of gas.

(E) A gas sample is cooled, andthe volume is increased.

14. The kinetic molecular theorypredicts that at a giventemperature

(A) all gas molecules have thesame kinetic energy

(B) all gas molecules have thesame average velocity

(C) only real gas moleculescollide with each other

(D) on the average, heaviermolecules move more slowly

(E) elastic collisions result in theloss of energy

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286 AP Chemistry

15. The effect that increasing the 19. Under identical conditions gaseoustemperature has on the pressure CO2 and CCl4 are allowed to effusemay be explained by the kinetic through a pinhole. If the rate ofmolecular theory as due to effusion of the CO2 is 6.3 X

(A) the increase in force with 10-2 mol s-\ what is the rate of

which the gas molecules effusion of the CCli

collide with the container (A) 6.3 X 10-2 mol S-1walls (B) 2.2 X 10-1 mol S-1

(B) the increase in rotational (C) 1.8 X 10-2 mol S-1energy of the gas molecules (D) 3.4 X 10-2 mol S-1

(C) the increase in averagevelocity (E) 1.2 X 10-1 mol S-1of the gas molecules, which 20. A gas has a density, at STp, ofcauses a corresponding increase 3.48 g L-1. The most reasonablein the frequency of collisions formula for this compound iswith the container walls

(D) a decrease in the attractive (A) C2H6forces between gas molecules (B) HF

(E) a combination of (A) and (C) (C) CCl4

16. Ideal gases(D) C6H6(E) CaF2·

(A) have no volume 21. The number of moles of an ideal(B) have no mass gas in a 2.50-L container at 300 K(C) have no attractive forces and a pressure of 0.450 atm isbetween them (R = 0.0821 L atm mol-1 K-1)

(D) have a combination of (A) and(C) (A) 0.0457

(E) have a combination of (A) and (B) 21.9(B) (C) 4.93 X 10-5

Under which conditions will a real(D) 2.03 X 104

17. (E) 6.02gas behave most like an ideal gas?

(A) high pressure and high22. A gas mixture contains twice as

many moles of 02 as N2. Additiontemperature of 0.200 mol of argon to this(B) low pressure and low mixture increases the pressure from. temperature 0.800 atm to 1.10 atm. How many

(C) low volume and high moles of 02 are in the mixture?temperature

(D) low pressure and high (A) 0.355temperature (B) 0.178

(E) high pressure and low (C) 0.533temperature (D) 0.200

18. Compared to ideal gases, real gases(E) 0.0750

tend to have

(A) larger volumes(B) greater kinetic energies(C) lower average kinetic energies(D)lower pressures(E) both (A) and (D)

23. A gas in a 1.50-L container has apressure of 245 mm Hg. When thegas is transferred completely to a350. rnl. container at the sametemperature, the pressure will be

I CHALLENGE I25. What volume of hydrogen gas, at

STp, will a 0.100-g sample ofmagnesium (molar mass = 24.31)produce when reacted with anexcess of H Cl?(Mg + 2HCI-7 MgCl2 + H2)

(A) 92.1 mL(B) 46.1 mL(C) 184 mL(D) 9.2 mL(E) 4.6 L

(A) 1.05 mm Hg(B) 1.05 atm(C) 2.14 mm Hg(D) 1050 mm Hg(E) 9.5 X 10-4 atm

24. At STP a 5.00-L flask filled withair has a mass of 543.251 g. The airin the flask is replaced with anothergas, and the mass of the flask isthen determined to be 566.107 g.The density of air is 1.290 g L-1.What is the gas that replaced theair?

(A) Ne(B) 02(C) Ar-(D) Xe(E) He

ANSWER KEY

LA 6. A 11. B 16. D 21. A2. D 7. C 12. B 17. D 22. A3. B 8. D 13. B 18. E 23. D4. A 9. D 14. D 19. D 24. D5. A 10. B 15. E 20. D 25. A

See Appendix 1 for explanations of answers.

Free-ResponseAnswer the following questions concerning the properties of gases and the theoriesused to explain their behavior.

(a) Describe an ideal gas and compare it to a real gas. Why do many real gasesbehave as ideal gases?

(b) The kinetic molecular theory is used to explain the behavior of gases.Briefly describe this theory and two of its applications to gases.

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312 AP Chemistry

5. Which of the followingcompounds will NOT formhydrogen-bonds?

(A) CH2F2(B) CH30H(C) H2NCH2CH2CH3(D) HOCH2CH20H(E) HClO

Practice Exercises

Multiple-Choice1. In which of the following are theintermolecular forces listed fromthe weakest to the strongest?

(A) dipole-dipole> London> hydrogen bonds

(B) London < dipole-dipole< hydrogen bonds

(C) hydrogen bonds <dipole-dipole < London

(D) London> hydrogen bonds> dipole-dipole

(E) London < hydrogen bonds< dipole-dipole

2. Which of the followingconsistently have the highestmelting points?

(A) metals(B) salts(C) molecular crystals(D) alkanes(E) hydrogen-bonded compounds

3. Which physical transformationoccurs in the process calledsublimation?

(A) gas to liquid(B) gas to solid(C) solid to liquid to gas(D) solid to gas(E) solid to liquid

4. Which element is expected to havethe greatest polarizability?

(A) Fe(B) Ca(C) Ne(D) S(E) Al

6. When the following compoundsare kept at the same temperature,the compound expected toevaporate most quickly is

(A) CSHlS(B) CgH170H(C) CgH17NH2(D) C6H14(E) C7H15COOH

7. Which of the following will havethe greatest change in its boilingpoint if the pressure at which it isboiled is changed from 1.00 atm to0.900 atm? (The numbers inparentheses are the heats ofvaporization in kilojoules per mole.)

(A) water (43.9)(B) ammonia (21.7)(C) methane (8.2)(D) bromine (15.0)(E) fluorine (5.9)

8. Which of the following statementsis NOT consistent with the crystalproperties of the substance?

(A) SiC is used to grind metalparts to shape.

(B) Tungsten is drawn into thinwires.

(C) Aluminum is used to cut glass.(D) Graphite is used to lubricate

locks.(E) MgF2 shatters when dropped.

9. What causes C30H62 to be anonpolar compound that is asolid at room temperature?

(A) ionic attractive forces(B) dipole-dipole attractions(C) London forces(D) the fact that the C30H62 is a

very heavy molecule(E) hydrogen bonding involving

the 62 hydrogen atoms

Liquids and Solids 313

10. Which physical property can bedetermined if the unit cell and itsdimensions are determined byX ray diffraction?

(A) heat capacity(B) heat of fusion(C) boiling and melting points(D) vapor pressure(E) density

Questions 11 and 12 refer to the heating curve below.

~:::J B.P. :~ 0001I(- - - - ~ - - - - -:- - - - - -7-----'1ID • .0.

E(!:. M.P.

0001I(- - - -7---~

SolidHeating

SolidMelting

LiquidHeating

Liquid GasBoiling Heating

Heat added (J)

11. On the basis of this heating curve, which of the following statements is true? .

(A) The heat of fusion and heat of vaporization are about equal.(B) The heat capacities of the solid, liquid, and gas are approximately equal.(C) The heat capacity of the gas is greater than that of the liquid.(D) The heat capacity of the gas is greater than the heat of fusion.(E) The heat of vaporization is much less than the heat of fusion.

12. On the basis of this heating curve, which of the following statements iscorrect about the substance?

(A) The substance supercools easily.(B) The gas is a metastable state.(C) The substance must be a salt that dissociates on heating.(D) The density of the liquid is greater than that of the solid.(E) The specific heat can be determined if the mass is known.

314 AP Chemistry

Questions 13-16 refer to the phase diagram below.

2.00

1.50E~~::l 1.00 .CfJCfJ~a.0.50

0.000L---5-0--1-0-0--15-0---?0-0---2-50-

Temperature rC)

13. Determine, from the phasediagram, the maximumtemperature at which thiscompound will sublime.

(A) 100 DC(B) 230 DC(C) 115 DC(D) 95 DC(E) It cannot sublime.

14. What is the normal boiling pointof this compound?

(A) 95 DC(B) 100 DC(C) 50 DC(D) 180 DC(E) 150 DC

15. At 125 DC and 1.50 atm ofpressure this substance will be

(A) a liquid(B) a solid(C) a gas(D) a solid and liquid in

equilibrium(E) a gas and liquid in equilibrium

16. Which pair of temperatures andpressures will produce asupercritical fluid?

(A) 150 DC and 2.00 atm(B) 95 DC and 1.00 atm(C) 145 DC and 230 atm(D) 10 DC and 0.15 arm(E) 250 DC and 2.00 atm

I CHALLENGE I17. A student observed that a small

amount of acetone sprayed on theback of the hand felt very coolcompared to a similar amount ofwater. Your explanation of thisphenomena should be that

(A) all organic compounds do this(B) acetone has a lower viscosity

and transfers heat quanta better(C) water has a higher heat

capacity than acetone,therefore retaining more heat

(D) the higher vapor pressure ofacetone results in more rapidevaporation and heat loss

(E) the observed effect is not realand is only imagined

Liquids and Solids 315

18. When a beaker of ethanol boilson the stove, small bubbles format the bottom of the beaker andrise to the 'surface. What isinside these bubbles?

(A) steam(B) hydrogen gas(C) oxygen gas(D) ethanol vapor(E) air

19. Diamond is classified as

(A) a covalent crystal(B) an ionic crystal(C) an amorphous solid(D) a metallic crystal(E) a molecular crystal

I CHALLENGE I20. A liquid substance that exhibits

low intermolecular attractions isexpected to have

(A) low viscosity, low boilingpoint, and low heat ofvaporization

(B) high viscosity, low boilingpoint, and low heat ofvaporization

(C) low viscosity, high boilingpoint, and low heat ofvaporization

(D) low viscosity, low boilingpoint, and high heat ofvaporization

(E) high viscosity, high boilingpoint, and high heat ofvaporization

ANSWER KEY1. B2. B3. D4. A

5. A6. D7. A8. C

9. C10. E11. A12. E

13. D14. D15. A16. E

17. D18. A19. A20. A

ee Appendix 1 for explanations of answers.

Free-Responsese the concepts and information in this chapter and in preceding chapters toanswer the following questions.

(a) Why must helium be cooled to 4 K before it will condense? Explain youranswer using fundamental concepts.

(b) Use the concepts in this chapter to explain why trans fats are consideredharmful whereas cis fats are not;

(c) Use a phase diagram to illustrate why carbon dioxide sublimes.

(d) Sketch a plot of boiling points versus period number for the hydrides ofthe oxygen group, the nitrogen group, and the halogen group. Explainwhat this demonstrates.