Page 64 - Physical chemistry eng

NUMERICAL PROBLEMS 41

Conceptual Problems

Q2.1 Electrical current is passed through a resistor Q2.13 A chemical reaction occurs in a constant volume
immersed in a liquid in an adiabatic container. The tempera- enclosure separated from the surroundings by diathermal
ture of the liquid is varied by 1°C. The system consists solely walls. Can you say whether the temperature of the surround-
of the liquid. Does heat or work flow across the boundary ings increases, decreases, or remains the same in this
between the system and surroundings? Justify your answer. process? Explain.
Q2.2 Two ideal gas systems undergo reversible expansion Q2.14 Explain the relationship between the terms exact
under different conditions starting from the same P and V. At the differential and state function.
end of the expansion, the two systems have the same volume.
Q2.15 In the experiment shown in Figure 2.4b, the weight
The pressure in the system that has undergone adiabatic expan-
drops in a very short time. How will the temperature of the
sion is lower than in the system that has undergone isothermal
water change with time?
expansion. Explain this result without using equations.
Q2.16 Discuss the following statement: If the temperature
Q2.3 You have a liquid and its gaseous form in equilibrium
of the system increased, heat must have been added to it.
in a piston and cylinder assembly in a constant temperature
Q2.17 Discuss the following statement: Heating an object
bath. Give an example of a reversible process.
causes its temperature to increase.
Q2.4 Describe how reversible and irreversible expansions
Q2.18 An ideal gas is expanded reversibly and adiabati-
differ by discussing the degree to which equilibrium is main-
cally. Decide which of q, w, ¢U , and ¢H are positive, nega-
tained between the system and the surroundings.
tive, or zero.
Q2.5 For a constant pressure process, ¢H = q P . Does it
Q2.19 An ideal gas is expanded reversibly and isother-
follow that q is a state function? Explain.
P
mally. Decide which of q, w, ¢U , and ¢H are positive, nega-
Q2.6 A cup of water at 278 K (the system) is placed in a
tive, or zero.
microwave oven and the oven is turned on for 1 minute during
which the water begins to boil. State whether each of q, w, Q2.20 An ideal gas is expanded adiabatically into a vac-
and ¢U is positive, negative, or zero. uum. Decide which of q, w, ¢U , and ¢H are positive, nega-
tive, or zero.
Q2.7 In the experiments shown in Figure 2.4a and 2.4b,
¢U surroundings 6 0 , but ¢T surroundings 7 0 . Explain how this Q2.21 A bowling ball (a) rolls across a table, and (b) falls
is possible. on the floor. Is the work associated with each part of this
process positive, negative, or zero?
Q2.8 What is wrong with the following statement? Burns
caused by steam at 100°C can be more severe than those Q2.22 A perfectly insulating box is partially filled with
caused by water at 100°C because steam contains more heat water in which an electrical resistor is immersed. An external
than water. Rewrite the sentence to convey the same informa- electrical generator converts the change in potential energy of
tion in a correct way. a mass m that falls by a vertical distance h into electrical
energy that is dissipated in the resistor. What value do q, w,
Q2.9 Why is it incorrect to speak of the heat or work asso-
and ¢U have if the system is defined as the resistor and the
ciated with a system?
water? Everything else is in the surroundings.
Q2.10 You have a liquid and its gaseous form in equilib-
Q2.23 A student gets up from her chair and pushes a stack of
rium in a piston and cylinder assembly in a constant tempera-
books across the table. They fall to the floor. Is the work asso-
ture bath. Give an example of an irreversible process.
ciated with each part of this process positive, negative, or zero?
Q2.11 What is wrong with the following statement? Because
the well-insulated house stored a lot of heat, the temperature Q2.24 Explain why ethene has a higher value for C V,m at
didn’t fall much when the furnace failed. Rewrite the sentence 800 K than CO.
to convey the same information in a correct way. Q2.25 Explain why C P,m is a function of temperature for
Q2.12 Explain how a mass of water in the surroundings can ethane, but not for argon in a temperature range in which
be used to determine q for a process. Calculate q if the tempera- electronic excitations do not occur.
ture of a 1.00 kg water bath in the surroundings increases by Q2.26 What is the difference between a quasi-static process
1.25°C. Assume that the surroundings are at a constant pressure. and a reversible process?

Numerical Problems

Problem numbers in red indicate that the solution to the prob- gas is compressed by placing a 725 kg mass on the piston of
lem is given in the Student’s Solutions Manual. diameter 25.4 cm. Calculate the work done in this process and
P2.1 A 3.75 mole sample of an ideal gas with C V,m = 3R>2 the distance that the piston travels. Assume that the mass of
initially at a temperature T = 298 K and P = 1.00 bar is the piston is negligible.
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enclosed in an adiabatic piston and cylinder assembly. The