che254 class practice exam

1. CHE 254 “Chemical Engineering Calculations”
Exam #1
Name: _________________________________
1. The density of a fluid is given by the empirical equation
ρ = 1000 exp(1.00x10‐4 P)
where ρ is density (kg/m3) and P is absolute pressure (mmHg).
a. (5 points) What are the units of 1000 and 1.00x10‐4?
b. (10 points) Use a single dimensional equation to calculate the density in lbm/ft3 for a
pressure of 20 psia.
2. Methanol flows at 1.10 kg/s through a 4.0 in (inner diameter) pipe. The density of methanol
is 0.792 g/cm3 and the viscosity is 0.500 cP (one centipoise (cP) is 10‐3 kg/m∙s). The Reynolds
number is
Re = d v ρ/μ
where d is the pipe inner diameter, v is the linear velocity, ρ is the density, and μ is the
viscosity.
a. (10 points) Calculate Re with a single dimensional equation.
b. (5 points) Check your answer with an order‐of‐magnitude estimation.

2. 3. The temperature in a process storage tank was measured over the course of an hour.
Time T(oC)
1:00 29
1:15 31
1:30 34
1:45 30
2:00 35
Calculate the statistical functions for this data using the equations described in your textbook
(show work). Do not use statistical functions on your calculator other than to check your
answer. Use the extra columns as necessary.
a. (5 Points) Mean
b. (5 Points) Range
c. (5 Points) Variance
d. (5 Points) Standard Deviation
e. (5 Points) 95% of the values should fall within two standard deviations. Do any of these data
fall outside this range?

3. 4. (15 points) A chemical reaction A → P takes place at a constant temperature. The rate of
chemical P formation is given by
CP = CA0 (1 – e‐kt)
where CP is the concentration of P (mol/L), CA0 is the initial concentration of A (4.83 mol/L), k is
the rate constant (s‐1), and t is the time (s). The following data was taken at BamaChem over
the holiday weekend.
t (s) CP (mol/L)
0 0
60 1.51
120 2.62
240 3.91
360 4.3
Plot this data as a straight line and label the graph in a professional manner. Find the rate
constant. (Use the extra columns as necessary.)

4. 5. A mixture containing 40 weight % water and 60 weight % ethanol flows through a 10 cm
(inner diameter) pipe at 100 kg/min. Physical properties of water: 18 g/mol, 1.0 g/cm3, and for
ethanol: 46 g/mol, 0.79 g/cm3.
a. (5 Points) What is the composition in mol%?
b. (5 Points) What is the total molar flow rate (mol/min)?
c. (5 Points) What is the volumetric flow rate (m3/min)?
d. (5 Points) What is the linear flow rate (m/min)?
6. (10 Points) Methane is flowing through a 12 inch pipe with an orifice plate. A manometer is
connected to pressure taps before and after the plate. The manometer fluid is a red‐dyed oil
of density 2.5 g/cm3. The difference between high and low ends of the manometer fluid is 24
cm. What is the pressure drop (difference) in mm Hg? Be sure to sketch and label the system.

5. HONOR PLEDGE: “I have neither given nor received unauthorized aid on this test.”
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