Chemistry 113 Quiz 2

January 25, 2001 Name ______________________________

Matching: Place the letter corresponding to the word(s) being defined in front of each of the following. (3)

_G__ 1. The ease of distortion of the electron cloud of an atom or molecule by an outside influence.

_F__ 2. Weak attractive forces caused by instantaneous dipole-induced dipole interactions.

_A__ 3. Description for the temperature at which the vapor pressure of a liquid equals atmospheric pressure.

_H__ 4. The conversion of a solid directly into a gas without passing through the liquid state.

_B__ 5. The temperature above which a substance cannot exist as a liquid regardless of the pressure.

_J__ 6. A measure of the energy needed to expand the surface area of a liquid.

  1. Boiling point D. Fusion G. Polarizability K. Triple point
  2. Critical E. H-bonding H. Sublimation L. Vaporization
  3. Dipole-dipole F. London forces I. Supercritical fluid M. Viscosity

J. Surface tension N. Wetting

Multiple Choice: Place the letter(s) corresponding to the best answer(s) in front of each of the following. (6)

A.B.C 7. The type of intermolecular force(s) that ethyl alcohol, H3C-C(H)2OH is expected to exhibit is (are)

A. Dipole-dipole B. H- bonding C. London

_A__ 8. The molecule(s) that is (are) expected to exhibit only London forces is (are)

A. CH4 B. H3COH C. H3CCl D. H2CF2

_B__ 9. The substance that is expected to have the highest normal boiling point. H-Bonding more

important than MW

A. CH4 B. H3COH C. H3CCl D. H2CF2

_D__ 10. At a given temperature the substance that is expected to have the highest vapor pressure is

A. CCl4 B. HCCl3 C. H2CCl2 D. H3CCl

_C__ 11. The property whose magnitude must always increase with increasing temperature is

A. density B. surface tension C. vapor pressure D. viscosity

_C,D 12. The following factor(s) that is (are) expected to affect the vapor pressure of a liquid is (are)

    1. The size of the container in which the liquid-vapor equilibrium is established
    2. The volume of the liquid in the liquid-vapor equilibrium
    3. The intermolecular forces in the liquid
    4. The temperature of the container at equilibrium

 

  1. Freon-12, CCl2F2, was used extensively as a refrigerant until the ozone hole led to its phase out. Its heat of vaporization is 289 J/g. What mass of Freon-12 must evaporate in order to freeze 100 g of water initially at 18oC. (DHfus for water = 334 J/g; the specific heat of water is 4.184 J/g K.) (3)

    2. To cool to f.p. water = mass x sp ht x DT = 100 g x 4.184 J/g deg x 18 deg = 7531.2 J

    To freeze water = mass x DHfus = 100 g x 334 J/g = 33,400 J

    Heat removed from water: 40,931.2 J = Heat absorbed by the freon = mass x DHvap = mass x 289 J/g

    Mass = 40931.2 J/289 J/g = 141.6 g = 142 g

    (note there is no need to use MW because units cancel without need for mol)

    g Freon = |_142 g_

     

  2. The temperature inside a pressure cooker is 115oC. What is the vapor pressure of water inside the pressure cooker at this temperature? (DHvap for water = 41.2 kJ/mol) (4)

    3. ln (p1/p2) = (DHvap / R) (1/T2 - 1/T1) ; normal b.p water = 100oC at 1.00 atm = 760 torr

    ln (p1/ 760 torr) = (41.2 kJ/mol x 1000 J/kJ / 8.314 J/mol deg) ( 1/373 - 1/388) =

    4.9555 x 103 ( 1.0365 x 10-3) = 0.5136

    p1 / 760 torr = inv ln 0.5136 = 1.6713

    p1 = 1.6713 x 760 torr = 1.2702 x 103 torr

     

    v.p. = |_1.67 atm_

    or 1.27 x 103 torr

  3. Use the phase diagram for helium to answer the following questions. Explain briefly if necessary. (4)
  1. What is the normal boiling point for He?

    2. Going across phase diagram at 1 atm to intersect liquid He-1 and vapor curve and then down to temperature, Read ~ 5.5K
  2. What is the normal freezing point for He?

    3. There is none because the solid does not exist at 1 atm pressure.

     

  3. What phases are present at the two triple points?

    4. Solid + liquid He-I and liquid He-II

    Gas + liquid He-I and liquid He-II

    (Note you need three phases or it would not be a triple point.)

  4. Is helium I or helium II denser?

He-I is denser. As pressure is increased (to form the denser form), He -II is changed to He-I.

 

Bonus. Will water rise to a greater height by capillary action in a glass tube or in a polyethylene tube of the same diameter? Explain your reasoning. (1)

The glass has silicate groups with oxygens that the water can H-bond with.

The polyethylene is nonpolar so that the intermolecular attraction would be the weaker dipole-induced dipole interaction.

The water climbs the capillary tube by interacting with the walls of the tube. Thus it would rise higher in the glass tube.