Test Bank for Fundamentals
of Chemical Engineering
Thermodynamics 1st Edition
By Kevin Dahm, Donald Visco
(All Chapters 1-15, 100%
Original Verified, A+ Grade)
All Chapters Arranged Reverse: 15-1
This is The Only Original and
Complete Test Bank for 1st
Edition, All Other Files in the
Market are Fake/Old/Wrong
Edition.
,Dahm/Visco Fundamentals of Chemical Engineering Thermodynamics Chapter 15
1. An ammonia synthesis process works as follows: Fresh feed air and hydrogen are combined
with a recycle stream and the combined stream is compressed to 10 MPa. The compressed
stream enters a reactor, and a fraction of the entering nitrogen and hydrogen are converted into
ammonia. The reactor effluent, still at 10 MPa, enters a condenser. The liquid and vapor
streams leaving the condenser are in VLE. The liquid stream, which is almost pure ammonia,
is the product. A fraction of the vapor stream leaving the condenser is purged, while the rest is
recycled. Which of the following statements is accurate?
A. Raoult’s Law would be a reasonable way to model the VLE for ammonia in the
condenser.
B. Henry’s Law would be a reasonable way to model the VLE for oxygen in the
condenser.
C. If we increase the size of the reactor, allowing a larger fraction of the nitrogen and
hydrogen to be converted to ammonia, it won’t lead to an increase in the liquid
product flow rate, because the product flow rate is limited by the equilibrium
constraint in the condenser.
D. If we maintain the same flow rate of entering feeds, but we purge a smaller fraction of
the vapor leaving the condenser, then the mole fraction of oxygen in the purge stream
will go down.
E. None of the above are true.
Analysis:
A. Incorrect. Raoult’s Law incorporates the ideal gas law for vapor phase modeling. A
pressure of 10 MPa is far too high to be considered ideal.
B. Correct. The liquid stream is described as almost pure ammonia. Henry’s Law is
used to model a system in which a trace of gas dissolved in a liquid. It might well be
acceptable to assume the liquid is pure ammonia, but if one was going to account for
the presence of gases dissolved in the ammonia, Henry’s Law would indeed be a
reasonable way to model the VLE.
C. Incorrect. The “equilibrium constraint” in VLE involves mole fractions, not absolute
numbers of moles. If the flow rate of ammonia entering the condenser increases, then
the liquid product flow rate can increase without a change in the mole fraction of
ammonia in either the liquid or the vapor product.
D. Incorrect. The amount of oxygen purged (mol/time) essentially equals the amount of
oxygen entering at steady state, since none is consumed in the reaction and very little
leaves through the liquid product. If we lower the total flow rate of the purge stream,
then the mole fraction of oxygen in that stream, which is constant, will increase.
E. Incorrect. One of these statements is reasonable.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
,Dahm/Visco Fundamentals of Chemical Engineering Thermodynamics Chapter 15
2. An ammonia synthesis process normally works as follows: Fresh feed air and hydrogen
are combined with a recycle stream and the combined stream is compressed to 10 MPa.
The compressed stream enters a reactor, and the entering nitrogen and hydrogen are
converted into ammonia until the reaction reaches equilibrium. The reactor effluent, still
at 10 MPa, enters a condenser. The liquid and vapor streams leaving the condenser are in
VLE. The liquid stream, which is essentially pure ammonia, is the product. A fraction of
the vapor stream leaving the condenser is purged, while the rest is recycled.
There is a problem with the compressors and the pressures of the reactor and the
condenser both drop to 9 MPa. The fresh feed rate and the fraction of vapor leaving the
condenser that is purged each remain the same, as do the reactor and condenser
temperatures. The system reaches a new steady state at 9 MPa. Which of the following
would you NOT expect to be true at the new steady state (compared to normal
operation)?
A. The mole fraction of ammonia in the vapor being purged will be higher than in
normal operation.
B. The extent of reaction will be lower than in normal operation.
C. The mass flow rate of liquid product will be lower than in normal operation.
D. The composition of the purge stream will change, but its mass flow rate will remain
the same as in normal operation.
E. All of the above would be expected to occur.
Analysis:
A. Incorrect. The vapor pressure of ammonia is a function of temperature, and is
unchanged. We thus expect the partial pressure of ammonia to be essentially
unchanged, but a lower total pressure does indeed mean a higher mole fraction of
ammonia.
B. Incorrect. The lower pressure will not drive the reaction as far, hence ξ will be lower
than normal. The product, ammonia, is favored by higher pressure because there are
fewer moles of gas on the product side of the reaction.
C. Incorrect. The lower pressure will cause the reactor to generate less ammonia. There
will be less ammonia flowing into the condenser, but the vapor pressure of the
ammonia in the vapor phase is a function of temperature and will be unchanged.
Consequently the new steady state flow of liquid product will be lower than in normal
operation.
D. Correct. Steady state requires that all mass entering the system leave the system. So
if the purge stream was the only stream leaving the system, then its mass flow rate
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
, Dahm/Visco Fundamentals of Chemical Engineering Thermodynamics Chapter 15
would indeed need to be the same at both steady states. But there is also a liquid
product leaving. If the flow rate of liquid product decreases, then the flow rate of the
purge stream increases.
E. Incorrect. One of these is not a likely expectation.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
of Chemical Engineering
Thermodynamics 1st Edition
By Kevin Dahm, Donald Visco
(All Chapters 1-15, 100%
Original Verified, A+ Grade)
All Chapters Arranged Reverse: 15-1
This is The Only Original and
Complete Test Bank for 1st
Edition, All Other Files in the
Market are Fake/Old/Wrong
Edition.
,Dahm/Visco Fundamentals of Chemical Engineering Thermodynamics Chapter 15
1. An ammonia synthesis process works as follows: Fresh feed air and hydrogen are combined
with a recycle stream and the combined stream is compressed to 10 MPa. The compressed
stream enters a reactor, and a fraction of the entering nitrogen and hydrogen are converted into
ammonia. The reactor effluent, still at 10 MPa, enters a condenser. The liquid and vapor
streams leaving the condenser are in VLE. The liquid stream, which is almost pure ammonia,
is the product. A fraction of the vapor stream leaving the condenser is purged, while the rest is
recycled. Which of the following statements is accurate?
A. Raoult’s Law would be a reasonable way to model the VLE for ammonia in the
condenser.
B. Henry’s Law would be a reasonable way to model the VLE for oxygen in the
condenser.
C. If we increase the size of the reactor, allowing a larger fraction of the nitrogen and
hydrogen to be converted to ammonia, it won’t lead to an increase in the liquid
product flow rate, because the product flow rate is limited by the equilibrium
constraint in the condenser.
D. If we maintain the same flow rate of entering feeds, but we purge a smaller fraction of
the vapor leaving the condenser, then the mole fraction of oxygen in the purge stream
will go down.
E. None of the above are true.
Analysis:
A. Incorrect. Raoult’s Law incorporates the ideal gas law for vapor phase modeling. A
pressure of 10 MPa is far too high to be considered ideal.
B. Correct. The liquid stream is described as almost pure ammonia. Henry’s Law is
used to model a system in which a trace of gas dissolved in a liquid. It might well be
acceptable to assume the liquid is pure ammonia, but if one was going to account for
the presence of gases dissolved in the ammonia, Henry’s Law would indeed be a
reasonable way to model the VLE.
C. Incorrect. The “equilibrium constraint” in VLE involves mole fractions, not absolute
numbers of moles. If the flow rate of ammonia entering the condenser increases, then
the liquid product flow rate can increase without a change in the mole fraction of
ammonia in either the liquid or the vapor product.
D. Incorrect. The amount of oxygen purged (mol/time) essentially equals the amount of
oxygen entering at steady state, since none is consumed in the reaction and very little
leaves through the liquid product. If we lower the total flow rate of the purge stream,
then the mole fraction of oxygen in that stream, which is constant, will increase.
E. Incorrect. One of these statements is reasonable.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
,Dahm/Visco Fundamentals of Chemical Engineering Thermodynamics Chapter 15
2. An ammonia synthesis process normally works as follows: Fresh feed air and hydrogen
are combined with a recycle stream and the combined stream is compressed to 10 MPa.
The compressed stream enters a reactor, and the entering nitrogen and hydrogen are
converted into ammonia until the reaction reaches equilibrium. The reactor effluent, still
at 10 MPa, enters a condenser. The liquid and vapor streams leaving the condenser are in
VLE. The liquid stream, which is essentially pure ammonia, is the product. A fraction of
the vapor stream leaving the condenser is purged, while the rest is recycled.
There is a problem with the compressors and the pressures of the reactor and the
condenser both drop to 9 MPa. The fresh feed rate and the fraction of vapor leaving the
condenser that is purged each remain the same, as do the reactor and condenser
temperatures. The system reaches a new steady state at 9 MPa. Which of the following
would you NOT expect to be true at the new steady state (compared to normal
operation)?
A. The mole fraction of ammonia in the vapor being purged will be higher than in
normal operation.
B. The extent of reaction will be lower than in normal operation.
C. The mass flow rate of liquid product will be lower than in normal operation.
D. The composition of the purge stream will change, but its mass flow rate will remain
the same as in normal operation.
E. All of the above would be expected to occur.
Analysis:
A. Incorrect. The vapor pressure of ammonia is a function of temperature, and is
unchanged. We thus expect the partial pressure of ammonia to be essentially
unchanged, but a lower total pressure does indeed mean a higher mole fraction of
ammonia.
B. Incorrect. The lower pressure will not drive the reaction as far, hence ξ will be lower
than normal. The product, ammonia, is favored by higher pressure because there are
fewer moles of gas on the product side of the reaction.
C. Incorrect. The lower pressure will cause the reactor to generate less ammonia. There
will be less ammonia flowing into the condenser, but the vapor pressure of the
ammonia in the vapor phase is a function of temperature and will be unchanged.
Consequently the new steady state flow of liquid product will be lower than in normal
operation.
D. Correct. Steady state requires that all mass entering the system leave the system. So
if the purge stream was the only stream leaving the system, then its mass flow rate
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
, Dahm/Visco Fundamentals of Chemical Engineering Thermodynamics Chapter 15
would indeed need to be the same at both steady states. But there is also a liquid
product leaving. If the flow rate of liquid product decreases, then the flow rate of the
purge stream increases.
E. Incorrect. One of these is not a likely expectation.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
