Exam 4, Fall, 2002
I. Multiple Choice (105 points) Select the best response for each of the following and record on the scantron. Do not erase; erasures may result in a misgrading of your response.
critical temperature and pressure of ammonia are 132°C and 111 atm respectively.
Under which of the following conditions will ammonia exist as a liquid?
a. 133°C and 111 atm
b. 132°C and 100 atm
c. 131°C and 1 atm
d. 131°C and 111 atm
e. none of the above, ammonia cannot exist as a liquid
2. Which of
the following statements correctly
correlates intermolecular forces with the observed property of a liquid?
Molecular systems with …
a. strong intermolecular forces have low critical temperatures.
b. weak intermolecular forces have low vapor pressures.
c. strong intermolecular forces have low enthaplies of vaporization.
d. weak intermolecular forces have low viscosities.
e. strong intermolecular forces have low melting points.
3. Real gases
have nearly ideal gas behavior at …
a. high temperatures and low pressures.
b. high temperatures and high pressures.
c. low temperatures and low pressures.
d. low temperatures and high pressures.
e. large numbers of moles and small volumes.
bonding occurs …
a. between all molecules containing a hydrogen atom.
b. between a hydrogen atom (covalently bonded to a N, O, or F) on one molecule and a N, O, or F of another molecule.
c. between a N, O, or F on one molecule and any or all hydrogens on another molecule.
d. between H2O and CH4 molecules.
e. between all molecules having a permanent dipole.
(skeletal structure is H–C–O–H) has a higher boiling point than CH3OCH3
(skeletal structure H–C–O–C–H) because …
a. CH3OH has dipole-dipole forces and CH3OCH3 does not.
b. CH3OH has stronger
c. CH3OH has lower molar mass than does CH3OCH3.
d. CH3OH has hydrogen bonding intermolecular forces and CH3OCH3 does not.
e. CH3OCH3 has
6. Equal, but
separate, volumes of Ar, CO2, and N2
exist at the same temperature and pressure.
What is true about the relationships between the gases?
a. The masses of the three gases are equal.
b. The number of molecules of the three gases are equal.
c. The number of moles of gas increase from N2 to Ar to CO2.
d. The number of moles of gas increase from CO2 to Ar to N2.
e. The masses of gas increase from CO2 to Ar to N2.
7. The boiling
point of several substances are listed. Which of the substances has the highest vapor
pressure at a given laboratory temperature?
a. I2: b.p.= 184°C
b. HF: b.p. = 20°C
c. NH3; b.p. = –33°C
d. CCl4; b.p. = 77°C
e. C6H6: b.p.= 80°C
8. Following are four properties of gases:
i. gases diffuse
ii. gas molecules exert pressure
iii. gas molecules are in rapid, random, straight‑line motion
iv. the average kinetic energy of gas molecules is constant at a given temperature
Which of these four statements are also true of solids?
a. ii and iv only
b. iii and iv only
c. ii, iii, and iv only
d. i and iii only
e. i, ii, iii, and iv
9. The phase diagram (P vs. T) at right is for a pure substance. Identify the point at which equilibrium
exists between the liquid and vapor phases of the substance.
10. A gas is confined to a vessel at a given pressure and
temperature. The gas is then transferred
to a vessel where the volume of the gas is tripled (in milliliters) and the
temperature of the gas is increased by a factor of 4 (in kelvins). By what factor has the pressure changed for
a. no change
b. decreased by a factor of 12
c. decreased by a factor of ¾
d. increased by a factor of 12
e. increased by a factor of 4/3
11. Identify the
molecule having the greatest velocity at a given temperature.
e. all have the same velocity
12. Two flasks of
volumes V1 and V2 (V2>V1)
contain the same number of helium atoms at the same temperature. Which of the following statement(s) is true?
a. The average velocity of the helium atoms in flask 1 is greater than those in flask 2.
b. The pressure exerted by the helium gas in flask 1 is greater than that in flask 2.
c. The pressure exerted by the helium gas in flask 1 equals that of flask 2.
d. The average kinetic energy of the helium atoms in flask 1 is lower than those of flask 2.
e. The intermolecular forces for the helium atoms in flask 2 is greater than those of flask 1.
13. Which of the
following molecules has the predicted highest boiling point?
14. Water “beads” on a wax surface.
The best explanation for this observation is that
a. the cohesive forces between water molecules are greater than the adhesive forces between water and wax.
b. the cohesive forces between water molecules are less than the adhesive forces between water and wax.
c. the wax molecules have a greater viscosity that water molecules.
d. the surface tension of the wax molecules is greater than that of the water molecules.
e. avocados are green and (most) apples are red.
statement regarding the effect of temperature on properties of liquids is incorrect? Increasing the temperature of
a. increases its vapor pressure.
b. decreases its surface tension.
c. increases its evaporation rate.
d. increases its standard enthalpy of vaporization.
e. decreases its viscosity.
16. Which of the
following is not a match of the type
of the solid for the corresponding substance?
a. covalent or network solid, C(graphite)
b. ionic solid, CuCl2
c. ionic solid, copper
d. molecular solid, CO2
e. metallic solid, gold
17. Tomorrow the Javelina football team participates in the 1st
round of the NCAA-II playoffs. Game time
is at noon and their opponents are from
a. the University of Texas
b. Bishop High School
c. the Texas Academy of Chemists
d. Texas A&M University at College Station
e. the University of Nebraska at Kearney
II. Exercises (60 points). The organization of all exercises must be shown clearly and legibly in order to receive any partial credit. Correct answers without a logical and systematic analysis and problem setup will receive only 10% credit.
1. (25 points) A 700.0 mL volume of SO2(g) at 1.40 atm
and 27.0°C is mixed with a 500.0 mL volume of O2(g) at 0.800 atm
also at 27.0°C. The following reaction
2 SO2(g) + O2(g) ® 2 SO3(g)
a. (15 pts) What is the partial pressure of SO3(g) when the reaction is complete? Assume a theoretical yield.
O2 is the limiting reactant; pso3 = 0.667 atm
b. (10 pts) Identify the excess reactant and determine its partial pressure.
SO2 is the excess reactant (by 7.30 x 10-3 mol); pso2 = 0.150 atm
2. (35 points) A 0.589 g sample
of an unknown gas is confined to a 300 mL reaction vessel at a pressure of
500 torr and a temperature of 44°C.
a. (10 pts) What pressure will the gas exert if the gas is transferred to a 1500 mL vessel at 22°C?
93.1 torr or 0.123 atm
b. (10 pts) What is the molar mass of the gas?
c. (5 pts) What is the density of the gas at STP?
3.47 g/L at STP
d. (10 pts) Will the diffusion rate of the gas be greater than or less than the rate of diffusion of xenon (molar mass = 131 g/mol)? By what factor? Your response must be substantiated!!
The diffusion rate of the gas will be greater by a factor of 1.30