Quiz 6
Chemistry 172 (2008-2009)
ln(P) = -
R = 8.314 J/mol x K
1)
3)
4)
5)
Hvap
1
x
+ C
R
T
Relative vapor pressures of liquids can be determined through the use of a barometer. Assign the following solvents to the
appropriate vapor height observed above a column of mercury in a barometer.
0.5 pts each
A) benzene (C6H6)
B) carbon tetrachloride (CCl4)
C) ethanol (CH3CH2OH )
27 mm __C____
2)
Name _____________________
280 mm ____B________
600 mm ____A____
Which of the following would be expected to have the indicated properties:
0.5 pts each
a) largest viscosity at a temperature where all are liquids
H2S
HF
CH4
b) highest boiling point
Cl2
Br2
I2
c) lowest freezing point
N2
CO
CO2
Which of the following is a good example of where strong adhesive forces would exist?
a) between two water molecules
b) between water and glass (SiO2)
c) between water and plastic
d) between ethane (CH3CH3) and glass (SiO2)
As the temperature of liquid ethanol (CH3CH2OH) is increased to its boiling point in a closed container, indicate whether the
following are true (T) or false (F)
0.5 pts each
a) the average kinetic energy of the CH3CH2OH molecules decreases
____F____
b) C-C covalent bonds are broken
____F____
c) the vapor pressure of the gas will increase
____T____
d) the ratio of CH3CH2OH molecules in the gas to liquid phase will increase
____T____
The atmospheric pressure in a cave, 2,000 ft below sea level is 816 mmHg and 429 mmHg at 15,000 ft above sea level. The
boiling point of an unknown substance is is 90 oC in the cave and and 72.5 oC at 15,000 ft. What is the enthalpy, in kJ/mol, of
this substance?
2 pts
𝒍𝒏
𝟒𝟐𝟗 𝒎𝒎𝑯𝒈
Insert values: 𝒍𝒏 𝟖𝟏𝟔 𝒎𝒎𝑯𝒈 = −
𝜟𝑯
𝑱
𝒎𝒐 𝒙 𝑲𝒍
𝟖.𝟑𝟏𝟒
𝟏
(𝟑𝟒𝟓.𝟓 −
𝟏
𝟑𝟔𝟑
𝑷𝟐
𝜟𝑯 𝟏
𝟏
= −
−
𝑷𝟏
𝑹 𝑻𝟐 𝑻𝟏
𝒂𝒏𝒅 − 𝟎. 𝟔𝟒𝟑 = −
𝜟𝑯
𝑱
𝒎𝒐𝒍𝒙𝑲
𝟖.𝟑𝟏𝟒
(𝟎. 𝟎𝟎𝟐𝟖𝟗𝟒 − 𝟎. 𝟎𝟎𝟐𝟕𝟓𝟓)
-5.346 = -ΔHvap(0.000139) and ΔHvap = 38,460 J/mol = 38.46 kJ/mol
6)
The enthalpy of vaporization for benzene is 30,900 J/mol. What would the numerical value of the slope be in a graph of
ln P vs 1/T for benzene?
slope =-ΔHvap/R = - 30,900 J/mol divided by 8.314 J/mol x K = -3717 K
7)
Which of the following is the best description of polarizability?
a)
b)
c)
d)
8)
refers to the magnitude of permanent charge on a molecule
refers to the relative temperature required to vaporize a liquid.
refers to the ease with which a cloud of electrons can be distorted
refers to the ease with which an electron can be removed from a molecule
In general, when comparing liquids at the same temperature, the liquid with the largest vapor pressure above it
would have the (
9)
highest
lowest
) melting point.
Of the following, which is the best definition of surface tension?
a) the ability of a liquid to resist dissolving a solid
b) resistance to an increase in volume
c) resistance to an increase in surface area
10)
Of the following, which is the best definition of “dynamic equilibrium” when applied to a liquid and the vapor phase above it.
a)
b)
c)
d)
11)
the number of molecules in the vapor and liquid phases are changing at a constant rate
the number in a phase is constant and molecules are in constant motion within each phase
there are equal numbers of molecules in the vapor and liquid phase
molecules are constantly moving between phases, but the number in each phase is constant.
The critical point is
a)
b)
c)
d)
e)
12)
d) resistance to conducting electricity
the highest temperature at which a solid can exist
the temperature at which pressure cannot convert a gas to a solid
the temperature at which super cooling will occur.
the temperature just before the vapor pressure equals atmospheric pressure.
the highest temperature at which a liquid can exist
Answer the following questions with respect to the phase diagram below.
1 pt each
a) What is the normal boiling point of the substance?
___222o C____
b) At what pressure would solid form if the substance at is 0.1 atm, temperature was maintained at 40 o C
and pressure increased.
___ 0.23 atm__
c) Below what pressure would sublimation occur?
__0.26 atm___
d) At what temperature do all phases co-exist?
_58o C____
e) Trace all portions of the line that show where freezing occurs.
0.28 to 1.18 atm
o
f) At what temperature will solid form if substance is at 250 C, pressure is maintained at 0.8 atm
and temperature decreased?
_85oC______