Sample Exercise 11.1 (p. 450) In which of the following substances is hydrogen bonding likely to play an important role in determining physical properties: methane (CH 4 ), hydrazine (H 2 NNH 2 ), methyl fluoride (CH 3 F), or hydrogen sulfide (H 2 S)? Practice Exercise 1 (11.1) Which of the following substances is most likely to be a liquid at room temperature? a) Formaldehyde, H 2 CO b) Fluoromethane, CH 3 F c) Hydrogen cyanide, HCN d) Hydrogen peroxide, H 2 O 2 e) Hydrogen sulfide, H 2 S Practice Exercise 2 (11.1) In which of the following substances is significant hydrogen bonding possible: methylene chloride (CH 2 Cl 2 ), phosphine (PH 3 ), hydrogen peroxide (HOOH), or acetone (CH 3 COCH 3 )? - 1 -
Sample Exercise 11.2 (p. 454) List the substances BaCl 2, H 2, CO, HF, and Ne in order of increasing boiling points. Practice Exercise 1 (11.2) List the substances Ar, Cl 2, CH 4, and CH 3 COOH in order of increasing strength of intermolecular attractions. a) CH 4 < Ar < CH 3 COOH < Cl 2 b) Cl 2 < CH 3 COOH < Ar < CH 4 c) CH 4 < Ar < Cl 2 < CH 3 COOH d) CH 3 COOH < Cl 2 < Ar < CH 4 e) Ar < Cl 2 < CH 4 < CH 3 COOH Practice Exercise 2 (11.2) a) Identify the intermolecular forces present in the following substances, and b) select the substance with the highest boiling point: CH 3 CH 3, CH 3 OH, CH 3 CH 2 OH. - 2 -
Sample Exercise 11.3 (p. 460) Calculate the enthalpy change upon converting 1.00 mol of ice at -25 o C to water vapor (steam) at 125 o C under a constant pressure of 1 atm. The specific heats of ice, water, and steam are 2.09 J/g-K, 4.18 J/g-K, and 1.84 J/g- K, respectively. For H 2 O, H fus = 6.01 kj/mol, and H vap = 40.67 kj/mol. (56.0 kj) Practice Exercise 1 (11.3) What information about water is needed to calculate the enthalpy change for converting 1 mol H 2 O (g) at 100 o C to H 2 O (l) at 80 o C? a) Heat of fusion b) Heat of vaporization c) Heat of vaporization and specific heat of H 2 O (g) d) Heat of vaporization and specific heat of H 2 O (l) e) Heat of fusion and specific heat of H 2 O (l) Practice Exercise 2 (11.3) What is the enthalpy change during the process in which 100.0 g of water at 50.0 o C is cooled to ice at -30.0 o C? (Use the specific heats and enthalpies for phase changes given in Sample Exercise 11.4.) (-60.4 kj) - 3 -
Sample Exercise 11.4 (p. 464) Use the figure below (Figure 11.25) to estimate the boiling point of diethyl ether under an external pressure of 0.80 atm. Practice Exercise 1 (11.4) In the mountains, water in an open container will boil when a) its critical temperature exceeds room temperature b) its vapor pressure equals atmospheric pressure c) its temperature is 100 o C d) enough energy is supplied to break covalent bonds e) none of these is correct Practice Exercise 2 (11.4) At what external pressure will ethanol have a boiling point of 60 o C? Vapor Pressure and Boiling Point Figure 11.25-4 -
Sample Exercise 11.5 (p. 466) Use the phase diagram for methane, CH 4, shown in Figure 11.30 (below) to answer the following questions. a) What are the approximate temperature and pressure of the critical point? b) What are the approximate temperature and pressure of the triple point? c) Is methane a solid, liquid, or gas at 1 atm and 0 o C? d) If solid methane at 1 atm is heated while the pressure is held constant, will it melt or sublime? e) If methane at 1 atm and 0 o C is compressed until a phase change occurs, in which state is the methane when the compression is complete? Practice Exercise 1 (11.5) Based on the phase diagram for methane (Figure 11.30, next page), what happens to methane as it is heated from -250 to 0 o C at a pressure of 10-2 atm? a) It sublimes at about -200 o C. b) It melts at about -200 o C. c) It boils at about -200 o C. d) It condenses at about -200 o C. e) It reaches the triple point at about -200 o C. Figure 11.30 Phase Diagram of Methane - 5 -
Practice Exercise 2 (11.5) Using the phase diagram of methane (above) to answer the following questions. a) What is the normal boiling point of methane? b) Over what pressure range does solid methane sublime? c) Above what temperature does liquid methane not exist? Sample Integrative Exercise (p. 470) The substance CS 2 has a melting point of -110.8 o C and a boiling point of 46.3 o C. Its density at 20 o C is 1.26 g/cm 3. It is highly flammable. a) What is the name of this compound? b) List the intermolecular forces that CS 2 molecules would have with each other. c) Write a balanced equation for the combustion of this compound in air. (You will have to decide on the most likely oxidation products.) d) The critical temperature and pressure for CS 2 are 552 K and 78 atm, respectively. Compare these values with those for CO 2 and discuss the possible origins of the differences. - 6 -