#2 WEBASSIGN Chapter 11 1. Arrange the following substances in the expected order of increasing boiling point: H2O, NH3, CH4, CH3CH3. (_) CH4 < CH3CH3 < H2O < NH3 (o) CH4 < CH3CH3 < NH3 < H2O (_) CH3CH3 < CH4 < NH3 < H2O (_) H2O < NH3 < CH3CH3 < CH4 Select the reasons for your ranking. (Select all that apply.) [x] NH3 has a higher boiling point than NH3CH3. [x] In H2O, hydrogen bonding is still stronger. [_] H2O, hydrogen bonding is weaker. [_] CH4 and CH3CH3 are polar. 2. At its normal boiling point, the enthalpy of vaporization of chloroform, CHCl3, is 247 J/g. (a) How many grams of CHCl 3 can be vaporized with 5.53 kJ of heat? [22.4] g
(b) What is Hvap of CHCl3 expressed in kilojoules per mole? [29.5] kJ/mol
(c) How much heat, in kilojoules, is evolved when 28.3 g CHCl3(g) condenses? [6.99] kJ
3. How much heat, in kilojoules, is required to melt a cube of ice that measures 5.60 cm on an edge? The density of ice is 0.92 g/cm3 and the enthalpy of fusion is 6.01 kJ/mol. [54] kJ
4. Which substance in each of the following pairs would you expect to have larger dispersion forces? (a) (_) C2H6 (ethane) (o) C8H18 (octane) (b) (_) HCl (o) HI (c) (_) H2O (o) H2Se
5. Which of the following substances would you expect to have a nonzero dipole moment? (Select all that apply.) [_] PCl5 [x] NF3 [x] CH3NH2 [_] XeF2
6. How much energy is released when 15.5 g of steam at 115.0C is condensed to give liquid water at 74.0C? The heat of vaporization of liquid water is 40.67 kJ/mol, and the molar heat capacity is 75.3 J/(Kmol) for the liquid and 33.6 J/(Kmol) for the vapor. [-37.1] kJ
7. The vapor pressure of SiCl 4 is 100 mm Hg at 5.4C, and the normal boiling point is 56.8C. What is Hvap for SiCl4 in kJ/mol? [3.0e+01] kJ/mol
8. Consider the following vapor pressure versus temperature plot for the three substances A, B, and C.
If the three substances are CH4, SiH4, and NH3, match each curve to the correct substance.
9. What pressure would have to be applied to steam at 345C to condense the steam to liquid water ( H vap = 40.7 kJ/mol)? [182] atm
10. Answer each of the following questions with increases, decreases, or does not change. (a) If the intermolecular forces in a liquid increase, what happens to the normal boiling point of the liquid? (o) increases (_) decreases (_) does not (b) change If the intermolecular forces in a liquid decrease, what happens to the vapor pressure of the liquid? (o) increases (_) decreases (_) does not change
(c) If the surface area of a liquid decreases, what happens to the vapor pressure? (_) increases (_) decreases (o) does not change (d) If the temperature of a liquid increases, what happens to the equilibrium vapor pressure? (o) increases (_) decreases (_) does not change
11. Which member of the following pairs has the stronger intermolecular dispersion forces? (a) (o) CH3CH2CH2CH2OH (_) (CH3)2CHCH2OH (_) neither of these (b) (o) CO2 (_) CO (_) neither of these (c) (o) CH3CH2CH2SH (_) CH3CH2SH 12. When KCl dissolves in water, what type of attractive forces must be overcome in the liquid water? (o) hydrogen bonds (_) chlorine bonds (_) potassium bonds (_) oxygen bonds When KCl dissolves in water, what type of forces must be overcome in the solid KCl? (o) ion-ion forces
(_) ion-dipole forces (_) dipole-dipole forces (_) induced dipole-induced dipole forces What type of attractive forces are formed when KCl dissolves in liquid water? (o) ion-dipole (_) induced dipole-induced dipole (_) ion-ion (_) dipole-dipole 13. Ethanol has the formula CH3CH2OH. Why does ethanol have a higher vapor pressure than water at a given temperature? (Select all that apply.) [x] ethanol has weaker intermolecular forces than water [_] ethanol forms more hydrogen bonds than water [_] ethanol is nonpolar [_] ethanol has stronger intermolecular forces than water [x] ethanol forms fewer hydrogen bonds than water [_] ethanol has a lower molar mass than water 14. 1.60 g of liquid methanol, CH3OH, is placed in an empty 20.0 L container at 45.0C. If the volume of the container is compressed to 2.40 L at 45.0C, how many grams of vapor are present? Assume the temperature remains constant and the volume of any liquid is negligible. The vapor pressure of methanol at 45.0C is 205 mm Hg. [0.794] g vapor
15. What type(s) of intermolecular force is (are) common to each of the following. (Select all that apply.) (a) Xe and menthanol (CH3OH) [x] London-dispersion forces [_] dipole-dipole [_] hydrogen bonding (b) CH3OH and acetonitrile (CH3CN) [x] London-dispersion forces [x] dipole-dipole [_] hydrogen bonding (c) NH3 and HF [x] London-dispersion forces [x] dipole-dipole [x] hydrogen bonding