402 | Thermodynamics
PROBLEMS*Entropy and the Increase of Entropy Principle
7–1C Does the temperature in the Clausius inequality rela-
tion have to be absolute temperature? Why?
7–2C Does a cycle for which dQ0 violate the Clausius
inequality? Why?
7–3C Is a quantity whose cyclic integral is zero necessarily
a property?
7–4C Does the cyclic integral of heat have to be zero (i.e.,
does a system have to reject as much heat as it receives to
complete a cycle)? Explain.
7–5C Does the cyclic integral of work have to be zero (i.e.,
does a system have to produce as much work as it consumes
to complete a cycle)? Explain.
7–6C A system undergoes a process between two fixed
states first in a reversible manner and then in an irreversible
manner. For which case is the entropy change greater? Why?
7–7C Is the value of the integral 12 dQ/Tthe same for all
processes between states 1 and 2? Explain.
7–8C Is the value of the integral 12 dQ/Tthe same for all
reversible processes between states 1 and 2? Why?
7–9C To determine the entropy change for an irreversible
process between states 1 and 2, should the integral 12 dQ/T
be performed along the actual process path or an imaginary
reversible path? Explain.
7–10C Is an isothermal process necessarily internally
reversible? Explain your answer with an example.
7–11C How do the values of the integral 12 dQ/Tcompare
for a reversible and irreversible process between the same
end states?
7–12C The entropy of a hot baked potato decreases as it
cools. Is this a violation of the increase of entropy principle?
Explain.
7–13C Is it possible to create entropy? Is it possible to
destroy it?
7–14C A piston–cylinder device contains helium gas. Dur-
ing a reversible, isothermal process, the entropy of the helium
will (never, sometimes, always) increase.
7–15C A piston–cylinder device contains nitrogen gas.
During a reversible, adiabatic process, the entropy of the
nitrogen will (never, sometimes, always) increase.
7–16C A piston–cylinder device contains superheated
steam. During an actual adiabatic process, the entropy of the
steam will (never, sometimes, always) increase.
7–17C The entropy of steam will (increase, decrease,
remain the same) as it flows through an actual adiabatic tur-
bine.
7–18C The entropy of the working fluid of the ideal Carnot
cycle (increases, decreases, remains the same) during the
isothermal heat addition process.
7–19C The entropy of the working fluid of the ideal Carnot
cycle (increases, decreases, remains the same) during the
isothermal heat rejection process.
7–20C During a heat transfer process, the entropy of a sys-
tem (always, sometimes, never) increases.
7–21C Is it possible for the entropy change of a closed sys-
tem to be zero during an irreversible process? Explain.
7–22C What three different mechanisms can cause the
entropy of a control volume to change?
7–23C Steam is accelerated as it flows through an actual
adiabatic nozzle. The entropy of the steam at the nozzle exit
will be (greater than, equal to, less than) the entropy at the
nozzle inlet.
7–24 A rigid tank contains an ideal gas at 40°C that is being
stirred by a paddle wheel. The paddle wheel does 200 kJ of
work on the ideal gas. It is observed that the temperature of
the ideal gas remains constant during this process as a result
of heat transfer between the system and the surroundings at
30°C. Determine the entropy change of the ideal gas.IDEAL GAS
40 °C200 kJHeat30 °CFIGURE P7–247–25 Air is compressed by a 12-kW compressor from P 1 to
P 2. The air temperature is maintained constant at 25°C during
this process as a result of heat transfer to the surrounding
medium at 10°C. Determine the rate of entropy change of the
air. State the assumptions made in solving this problem.
Answer:0.0403 kW/K*Problems designated by a “C” are concept questions, and students
are encouraged to answer them all. Problems designated by an “E”
are in English units, and the SI users can ignore them. Problems
with a CD-EES icon are solved using EES, and complete solutions
together with parametric studies are included on the enclosed DVD.
Problems with a computer-EES icon are comprehensive in nature,
and are intended to be solved with a computer, preferably using the
EES software that accompanies this text.