CHEM 341
PHYSICAL CHEMISTRY
EXAM 1
Do not open this exam until
told to do so. The exam consists
of 5 pages, including this one. Count
them to insure that they are all there.
Constants and
conversions:
R = 8.31 J K-1
mole-1 NA
= 6.02 x 1023 MWwater
= 18
CP (liquid
water) = 75.3 J K-1 mole-1 CP (ice) = 37.0 J K-1 mole-1
DHfus (water) = 6.01 kJ/mole 1 atm = 101325 Pa = 101325 J/m3
Page |
Score |
|
2 |
/24 |
|
3 |
/38 |
|
4 |
/19 |
|
5 |
/19 |
|
Total |
/100 |
Conceptual Problems
(each problem is worth 4 points).
1) Pressure can be thought of in terms of:
a) Force per unit area
b) Energy per unit volume
c) a and b
d) none of the above
2) The absolute temperature of a system is a measure of:
a) The density of molecules
b) The heat entering the system
c) The average kinetic energy of the molecules
d) The work a system is capable of performing
3) If heat is transferred reversibly from the environment to a system and nothing else changes, the entropy change of the system is:
a) Positive
b) Negative
c) Zero
d) Can’t tell from the data given
4) We say a system is adiabatic when:
a) No energy or matter can enter or leave the system
b) The volume of the system is fixed
c) Heat freely passes between the system and the surroundings
d) No heat can enter or leave the system
5) An endothermic reaction is one in which:
a) Heat is taken up by the reaction
b) Heat is released by the reaction
c) Heat freely passes between the system and the surroundings
d) No heat can enter or leave the system
6) For a spontaneous reaction, which of the following is true:
a) DSSys > 0
b) DHSys < 0
c) DSSys > q/T
d) DG > 0
7) At constant temperature and pressure, the Gibbs energy change (DG) of the system is always proportional to:
a) -DSSys
b) -DSSur
c) -DSTot
d) DSSys -DSSur
8) In the equation DG = DH - TDS (at constant pressure and temperature):
a) DG represents the Gibbs energy change of the system
b) DG represents the Gibbs energy change of the surroundings
c) DG represents the Gibbs energy change of the whole universe
d) DG represents the Gibbs energy change of the molecules in the reaction itself
Numerical Problems
(each problem is worth 14 points). All work must be shown for credit.
9)
What is the pressure of 0.1 moles of nitrogen
gas (assume it is ideal) in a 10 liter container at 25 C?
10) What is the
molar heat capacity of a 2 mole sample of liquid that rose in temperature by 10
C when supplied with 560 J of heat?
11) Calculate the
standard enthalpy of reaction for 2H2O2 (l) à 2H2O(l)
+ O2(g) at 50 C. The standard
enthalpy of the reaction at 25 C is –196.0 kJ/mole (this is per mole of O2). The molar heat capacity at constant pressure
of H2O2 (l) is 89.1 J K-1 mole-1,
for H2O(l) is 75.3 J K-1 mole-1 and for O2(g)
is 29.4 J K-1 mole-1
12) Consider the reversible, isothermal expansion of 6 moles of an ideal gas with an initial volume of 15 liters to 150 liters. The external pressure is 1 atm. The temperature is 25 C. Determine DU, w, q, DSSys, DSSur, DSTot.
Quasi Real World
Problem (12 points)
13) A large backyard swimming pool has about 100,000 liters of water in it. In Arizona in the summer time, it is often the case that the water in the pool gets warmer than most people like. One way of cooling the water down is to accelerate the evaporation of the water by spraying it in the air. The water sprayed in the air cools because some of it evaporates and then it falls back in the pool, cooling off the pool in general. How much water would have to evaporate from the pool in order to cool it by 5 C? Assume that the evaporation happens fast enough so you do not have to worry about any other source of heating or cooling. Also assume that the amount of water that has to be evaporated is small enough so you do not have to worry about the number of moles of water in the pool changing significantly. DHVap = 44 kJ/mole at 25 C (assume the water is at 25 C). One liter of water has a mass of 1 kg. The molecular weight of water is 18.