McMurry - Chemistry 8th Edition

Ch.11 - Liquids & Phase Changes

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McMurry 8th Edition

Ch.11 - Liquids & Phase Changes

Problem 15

Assume that you have a liquid in a cylinder equipped with a movable piston. There is no air in the cylinder, the volume of space above the liquid is 200 mL, and the equilibrium vapor pressure above the liquid is 28.0 mm Hg. What is the equilibrium pressure above the liquid when the volume of space is decreased from 200 mL to 100 mL at constant temperature?

Problem 18

A phase diagram for a substance that exhibits the liquid crystalline state is shown. (b) If the substance is at a temperature and pressure repre- sented by point 1 and the temperature is increased until the phase changes, what is the phase transition? Describe how the ordering of molecules changes, and propose a reason for the change.

Problem 19

The following compound undergoes a phase transition from the solid to the smectic liquid crystal phase at 121 °C. Upon further heating, the compound undergoes another transition to liquid phase at 131 °C.

(a) Which image represents the arrangement of molecules at 125 °C?

Problem 21

Water flows quickly through the narrow neck of a bottle, but maple syrup flows sluggishly. Is this different behavior due to a difference in viscosity or in surface tension for the liquids?

Problem 22

Predict which substance in each pair has the highest surface tension. (a) CCl4 or CH2Br2

Problem 23a

Predict which substance in each pair has the highest viscosity. (a) Hexane 1CH3CH2CH2CH2CH2CH32 or 1-hexanol 1CH3CH2CH2CH2CH2CH2OH2

Problem 23b

Predict which substance in each pair has the highest viscosity. (b) Pentane or neopentane

Problem 24

The chemical structure for oleic acid, the primary component of olive oil, is shown. Explain why olive oil has a higher vis- cosity than water.

Problem 25

The viscosity of water at 20 °C is 1.00 * 10-3 1N • s>m2 2 higher than dimethyl sulfide 31CH322 S4 2.8 * 10-4 1N • s>m2 2. Explain the difference in viscosity based on chemical structure.

Problem 27

Assume that you have a sample of gas at 350 K in a sealed container, as represented in (a). Which of the drawings (b)–(d) represents the gas after the temperature is lowered from 350 K to 150 K? The boiling point of the gas is 90 K.

Problem 29

What is the vapor pressure of SiCl4 in mm Hg at 30.0 °C? (See Problem 11.27.)

Problem 30

Dichloromethane, CH2Cl2, is an organic solvent used for removing caffeine from coffee beans. The following table gives the vapor pressure of dichloromethane at various tem- peratures. Fill in the rest of the table, and use the data to plot curves of Pvap versus T and ln Pvap versus 1/T.

Problem 31

The following diagram shows a close-up view of part of the vapor-pressure curves for a solvent (red curve) and a solution of the solvent with a second liquid (green curve). Is the second liquid more volatile or less volatile than the solvent?

Problem 32

The following phase diagram shows part of the liquid–vapor phase-transition boundaries for two solutions of equal con- centration, one containing a nonvolatile solute and the other containing a volatile solute whose vapor pressure at a given temperature is approximately half that of the pure solvent.

(d) Based on your drawing, what is the approximate normal boiling point of the pure solvent?

Problem 34

Choose any two temperatures and corresponding vapor pressures in the table given in Problem 11.30, and use those values to calculate ΔHvap for dichloromethane in kJ/mol. How does the value you calculated compare to the value you read from your plot in Problem 11.32?

Problem 35

The dipole moment of methanol is m = 1.70 D. Use arrows to indicate the direction in which electrons are displaced.

Problem 36

Dichlorodifluoromethane, CCl2F2, one of the chlorofluo- rocarbon refrigerants responsible for destroying part of the Earth's ozone layer, has Pvap = 40.0 mm Hg at -81.6 °C and Pvap = 400 mm Hg at -43.9 °C. What is the normal boiling point of CCl2F2 in °C?

Problem 37

Two dichloroethylene molecules with the same chemical formula 1C2H2Cl22, but different arrangements of atoms are shown.

Problem 39

Why is the heat of sublimation, ΔHsubl, equal to the sum of ΔHvap and ΔHfusion at the same temperature?

Problem 40

Naphthalene, better known as 'mothballs,' has bp = 218 °C and ΔH_vap = 43.3 kJ>mol. What is the entropy of vaporization, ΔS_vap in J/(K mol) for naphthalene?

Problem 44

Mercury has mp = -38.8 °C and bp = 356.6 °C. What,if any, phase changes take place under the following condi-tions at 1.0 atm pressure? (a) The temperature of a sample is raised from -30 °C to 365 °C.

Problem 46

How much energy in kilojoules is needed to heat 5.00 g of ice from -11.0 °C to °30.0 °C? The heat of fusion of water is 6.01 kJ>mol, and the m# olar heat capacity is 36.01 kJ>mol for ice and 75.4 J/K mol2 for liquid water

Problem 49

How much energy in kilojoules is released when 25.0 g of ethanol vapor at 93.0 °C is cooled to -11.0 °C? Ethanol has mp = -114.1 °C, bp = 78.3 °C, ΔHvap = 38.56 kJ>mol, and ΔHfusio#n = 4.93 kJ>mol. The molar heat#capacity is 112.3 J>1K mol2 for the liquid and 65.6 J>1K vapor.

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