CBE 205 -- Fall 2005
GUIDE FOR TEST 2
The test will be open book/closed notes and workbook and will cover through
Section 6.3. You are strongly advised to annotate your textbook with tabs,
highlight key equations, and add to the "Selected Tables and Figures"
list on the inside front cover.
- Everything on the previous
- "Test Yourself" questions and questions about
- Explanations. Be able to briefly and clearly
explain each of the following in your own words:
- Recycle (and its
purpose). Purge (and its
- Fractional conversion
of a limiting reactant. Percentage excess of a reactant. Theoretical air
and percent excess air in a combustion reactor. Dry basis composition of
a mixture containing water. Extent of reaction, yield, and selectivity.
- The statement
"Assume volume additivity" for a liquid mixture.
- The statement
"Assume ideal gas behavior." You should also be able to state
two ways to determine whether this assumption is a good one.
- STP. SCMH. Why
"350 m3(STP)/h of nitrogen at 25oC and 3.5
atm" looks like a contradiction but is not one.
- Partial pressure of a
gas mixture component. Percentage by volume (% v/v) of a gas mixture
component, e.g. 20% v/v CO. How to calculate the mole fraction of a
component of a gas mixture given either of the first two quantities and
the total pressure.
- The law of
corresponding states. The compressibility factor (Z).
Pseudocritical temperature and pressure. Kay's rule.
- A phase diagram.
Boiling and melting points and how they depend on pressure. The
difference between a gas and a vapor. Normal boiling point and normal
melting point. Triple point. Critical temperature and pressure. Where in
F&R you can look up normal boiling points, normal melting points, critical
temperatures and critical pressures.
- Vapor pressure and how
it depends on temperature. Two ways to determine from data in F&R the
vapor pressure(for a given T) or the boiling point (for a given P)
of certain species, and a third way if the species is water. How you can
tell which of two liquids is more volatile, and what that means.
- The Gibbs phase
rule--what it is and what information it gives you.
- Saturated vapor,
superheated vapor, dew point, degrees of superheat, relative saturation,
and relative humidity. How to calculate the mole fraction of a vapor in a
gas mixture given any of the last four quantities along with temperature,
total pressure, and an equation or data for vapor pressure.
- Why it takes longer to
make a hard-boiled egg at a ski resort than at the beach. Whether it
should take longer to boil an egg on a stormy day than on a sunny day,
and why.(The terms "atmospheric pressure" and "boiling
point" should appear in the explanations.)
- Multiple unit processes,
recycle, bypass, and purge. Given a process description, choose a
convenient basis of calculation, draw and completely label the flow
chart, identify the systems on which balances could be written, do the DOF
analysis for each system, write the equations you would use to calculate
specified process variables, and (maybe) perform the calculations. State
all assumptions you make.
- Balances on reactive
systems. Given a
description of a reactive process, assume a basis and draw and completely
label the flow chart, do the DOF analysis (basing it on molecular
balances, atomic balances, or extents of reaction as requested), write the
equations you would use to solve for unknown process variables using
either atomic balances or extents of reaction, and (maybe) perform the
calculations. State all assumptions you make.
- Combustion. Given information about a fuel
composition, assume a basis of calculation and calculate the feed rate of
air from a given percent excess or vice versa (given the percent excess
air, calculate the air feed rate). Given additional information about the
conversion of fuel and/or the wet-basis or dry-basis composition of the
exhaust gas, draw and completely label the flow chart, do the DOF
analysis, write the equations you would use to solve for unknown process
variables, and (maybe) perform the calculations. State all assumptions
- Ideal gas calculations. Given any three of the variables P,
V, T, and n (or any two of P, V^ and n)
for a gas, calculate the remaining variable directly from the ideal gas equation
of state or using conversion from standard conditions. Quickly determine
whether the error you will make by assuming ideal gas behavior is less
than 1%. Do the DOF analysis and solve material balance problems for
process systems in which one or more of the streams are ideal gases and
volumes are either given or requested. (Warning: If you label volume
fractions or try to do a volume balance you will lose major points!)
- Real gas calculations. Given any three of the variables P,
V, T, and n for a gas, outline how you would calculate the
fourth variable using the SRK equation of state or the compressibility
factor equation of state and the compressibility charts. Do the latter
calculation for a single species or for a mixture using Kay's rule.
- Phase behavior. Given a phase diagram for a species,
state what happens when a specified path is followed (like Path ABCDE on
Figure 6.1-1). The words "boiling point," "melting
point," "sublimation point," and "vapor pressure"
should appear when appropriate. Calculate volumes after every step of the
- Vapor pressure
determination. Given a
temperature of a pure species, look up or calculate the vapor pressure
from data in F&R. Given a pressure, look up or calculate the boiling
point. Do the latter the easy way if the pressure happens to be 1 atm.
- Behavior of a gas mixture containing a single
condensable species. Suppose you have a gas mixture containing a
single condensable species, A(v), for which the vapor pressure, pA*(T),
is given or can be calculated or looked up.
- Given any three of the quantities T,
P, yA (mole fraction), pA (partial
pressure), Tdp (dew point), DS (degrees of
superheat), and RS (relative saturation) or RH (relative
humidity) for the gas mixture, calculate all of the others. (Some
combinations may not work, like specifying T, Tdp, and DS,
since you can calculate any one from the other two).
- Given that the mixture is in equilibrium
with the liquid of the condensable species, calculate all of those
variables from given values of any two of the variables T, P, and yA.
Explain why any of the calculated values could be in error, assuming that
you did not make any mistakes. (In other words, what have you assumed?)
- Material balances on two-phase (vapor
mixture-pure liquid) systems with the outlet streams in equilibrium.
Suppose the liquid species is A and you are given saturation information (Tdp,
RH, DS, etc.) for the gas inlet stream. Draw and label the flow chart,
do the DOF analysis, write the equations, then (maybe) do the
calculations. State all assumptions you make.