CHEG 200: Chemical Engineering Principles
Study Guide for the Final Exam
Energy Balances without or with chemical reactions
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Select an appropriate form for the energy balance, either based on mass or mole.
Write the general form of the energy balance for either an open or closed system.
Apply assumptions like negligible changes in kinetic and potential energy, no reactions, adiabatic, and no shaft
work to simplify this general form.
Define the terms flow work and specific internal energy, volume, and enthalpy.
Write the specific enthalpy of any process stream (or material) in general form as a function of temperature,
pressure, and composition {i.e., H = hmix[T, P, comp]}.
Sketch the PH and PU diagrams for a typical pure component and choose its reference state.
Identify the single phases and equilibrium phases in these diagrams.
Trace a multi-step process in both diagrams.
Label each diagram with tabular data from the literature, such as boiling point, critical point, saturated liquid
and vapor molar or specific quantities.
Apply the reverse-lever rule in the two-phase regions of these diagrams.
Compare the tabular data in the steam tables to the PH and PU diagrams.
Analyze energy balance problems using a PH diagram or tabular PH or PU data.
Calculate the molar or specific enthalpy of multi-component process stream for an ideal solution (i.e., mixture is
equal to sum of its pure components).
Select a reference state (T, P, and stable phase) for a pure component, and calculate sensible energy changes
and latent energy changes that go from the reference state to the state of the process stream.
Derive why the reference state of a pure component can be arbitrarily selected for non-reacting systems.
Derive why the reference state for chemical reactions must be the pure elements at 25°C, and 1 atm, and their
stable phase.
Analyze material and energy balance problems that require the mixture enthalpies using tables, graphs, or
equations.
Remember that any basic relationship (=) on the green "gotche" table is fair game
on the Final Exam.
Any function (like psat, tsat, vlet, vlevf, vlep, umix, or hmix) can be represented by a table, graph,
equations, or computer program, in that order of complexity. Remember that a table is more
accurate than a graph, a graph is easier to use than solving equations, and equations that do not
involve iteration are to be use when a table or graph is not available. Obviously, equations with
iteration and computer programs are expected to be solved on homework problems but not on
exams.
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CHEG 200: Chemical Engineering Principles
Study Guide for the Final Exam
Energy Balance Analysis
a. Differential Energy Balance
energy unit/time {
continuous process }
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blue crib sheet for no chemical reactions; pink crib sheet for chemical reactions
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hmix [ temperature, pressure, composition ]
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hmix functional form:
for each process stream
graph, table, equation(s), or computer program
If hmix is for a pure substance, use Hˆ j function on appropriate crib sheet (Item D.7).
If hmix is for a mixture, use a graph when it is provided for the mixture.
If hmix is for a mixture, use a table when it is provided for the mixture.
If hmix is for a mixture, use enthalpy equation on appropriate crib sheet (Items C and D).
If hmix is for a mixture, use Aspen HYSYS for assigned project problems.
b. Integral Energy Balance
energy units only
{ batch, semi-batch, or continuous process }
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blue crib sheet for no chemical reactions; pink crib sheet for chemical reactions
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hmix [ temperature, pressure, composition ]
for each process stream
graph, table, equation(s), or computer program
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umix [ temperature, pressure, composition ]
(see hmix function above)
for final and initial state of system
If umix is for pure water, use steam tables (B.5, B.6, and B.7) for UˆWA .
If umix is for a pure substance other than pure water, then do one of the following:
For a solid or liquid,
For an ideal gas,
For real gas,
Uˆ j  Uˆ j T j , Pj , Ph j  
Uˆ j  Uˆ j T j , Pj , Ph j  

T
Tj
 Cˆ
T
Tj
Cˆ PPh, ji dT
ig
P, j
with Uˆ j  0

 R dT with Uˆ j  0
use Aspen HYSYS to find Uˆ j of pure substance j.
If umix is for a mixture, use a graph when it is provided for the mixture.
If umix is for a mixture, use a table when it is provided for the mixture.
If umix is for a mixture, use Items C and D on a crib sheet with Uˆ in place of Hˆ .
If umix is for a mixture, use Aspen HYSYS for assigned project problems.
Any functional form [ … ]: graph, table, equation(s), or computer program.
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CHEG 200: Chemical Engineering Principles
Study Guide for the Final Exam
Problem A
A Co-op Activity to be done in the Review Session
Yakonal, Inc has asked our department to determine the flow rate of cooling water (kg/s) needed to
cool a process stream of pure ethanol from 300°C and 2.1 atm to a saturated liquid state. The ethanol
stream flows at 152 kgmol/h. Cooling water is available at 31°C and can be heated to a maximum of
41°C. Assume that heat capacity of an organic compound is a linear function of temperature and
heats of vaporization at any pressure are the same as that at 1 atm. For ethanol, pick the saturated
liquid at 2.1 atm as the reference state for any enthalpy calculations. Sketch the PH diagrams for
ethanol and water.
Problem B
A Co-op Activity to be done in the Review Session
Yakonal, Inc has asked our department to approximate the exit temperature for an
adiabatic reactor where the feed enters at 420°C and 1.3 atm. The feed flows at 100
mol/s and contains 43.7 mole % ethylene, 26.3 mole % water, and the balance nitrogen.
The following hydration reaction only occurs in the reactor:
___ C2H4
ethylene
+
___ H2O
water

___ C2H5 OH
ethanol
with a 40 percent conversion of the ethylene. Sketch the PH diagrams for all chemical
components. Assume that heat capacity is not a function of temperature.
Click here for the Solutions to Problems C and D
Problem C
See Quest P4.W2F (yellow).
Note pp. 6-64 to 6-65 in CinChE
A process steam of pure ammonia at 46.85°C, 100.0 bar, and 125 kg/s is throttled through a valve to
an exit temperature of 240 K. Depict this flash operation on a sketched PH diagram for ammonia.
Using the reverse lever rule, what are the liquid fraction and flow rates of the exit vapor and liquid
streams? Also, what is the exit pressure in bar?
isenthalpic process
Problem D
See Ex. 7.6-3 in F&R, p. 332. Quest P4.W1W.b ( yellow Quiz 11Q.F )
Saturated steam at 1 bar is discharged from a turbine at a rate of 1150 kg/h. Superheated
steam at 300°C and 1 bar is needed as a feed to a heat exchanger; to produce it, the turbine
discharge stream is mixed with superheated steam available from a second source at 400°C
and 1 bar. The mixing unit operates adiabatically. Calculate the amount of superheated
steam at 300°C produced and the required volumetric flow rate of the 400°C steam. For a
velocity of 1.8 m/s, what is the pipe diameter in ft for the 400°C stream? Depict the mixing
operation on a sketched PH diagram for water.
simultaneous mat’l and energy balances
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