Name ___________________________
CEEGR 342 – Midterm 2 (100 points)
Multiple Choice (2 points each)
1. A batch reactor is used to determine reaction order. If a plot of LN(C/C0) vs. t is the most linear, what
order is this?
a) 0th
b) 1st
c) 2nd
d) 3rd
2. What does CSTR stand for?
a) Continuously Stirred Tank Reactor
c) Continuously Stable Tank Reactor b) Continuous Species Treatment Reactor
d) Continuously Steady Tracer Reaction 3. A batch reactor by definition ____________.
a) Is at steady-state
b) Has a first order reaction
c) Has no inflow or outflow
d) Operates faster than a PFR
4. Given a maximum specific growth rate = 5/d and saturation coefficient (concentration at halfmaximum growth rate) = 60 mg substrate/L, estimate the observed growth rate at a concentration of 20
mg substrate/L.
a) 1.3/d
b) 1.5/d
c) 3.8/d
d) 4/d
Short Answer
5. For a positive order reaction (non-zero), the volume requirement of a PFR is (less than/greater than)
the volume requirement of a CSTR to achieve the same extent of reaction? (1 point)
6. Photosynthesis raises pH in aquatic systems because the organisms use dissolved CO2 (or H2CO3) as
their carbon source. Why does this raise the pH? In other words, what happens to the aqueous H+ and
why? (2 points) 7. Write the correct solubility product equilibrium expression (Ksp = …) for Hg2Br2 (s). The Ksp = 6.4x10-23,
you should include the magnitude of this constant in your answer. (3 points) 8. Identify two ‘natural sources’ of carbonates in water. (2 points) 1
CEEGR 342 2013-14: Midterm 2 Name ___________________________
9. Biodegradation of PAH in a catch basin is observed to follow 0th order kinetics. The catch basin
operates as a ‘batch reactor’ in-between clean-outs. During one analysis, the PAH’s were initially at 15
mg PAH/kg solids but were reduced to 8 mg/kg after 1.5 months. During a second analysis they were
reduced from 9 mg/kg to 1 mg/kg after 2 months. Estimate how long it would take to reduce PAHs from
20 mg/kg to 5 mg/kg. (6 points) 10. The following diagram describes a membrane system. There is no reaction. Calculate the unknown
quantities. (4 points) 11. The equilibrium constant for dissociation of hypochlorous acid at 25°C = 3.2x10-8. Its enthalpy change
due to reaction = -89 kJ/mol rxn, its Gibbs free energy change due to reaction = +43 kJ/mol rxn. The
reaction is shown below. Estimate the equilibrium constant at 10°C. (6 points)
HOCl = OCl- + H+ 12. Calculate the mass of FeF2 (93.8 g/mol) that can be added to 10-L of water before it begins to
precipitate. (7) 2
CEEGR 342 2013-14: Midterm 2 Name ___________________________
Long Answer
13. A 20-L carboy of lake water is initially at pH = 6.4, and has HCO3- concentration = 15 mM. Strong base
(NaOH) is added to raise the pH to 11. What is the alkalinity after the pH is raised (i.e. at pH =11)? Show
all steps and units. (12 points) 14. An aqueous system is at pH=5.5, with HCO3- = 1.3 mM, H2CO3 = 2.7 mM, and CO32- = 0 mM.
Determine if the system is at equilibrium using Gibbs free energy, not by comparing Q/K. If it is out of
equilibrium, determine if the reaction will move in the direction written (LR), or opposite to the
direction written. Show all steps and units. (10 points)
H2CO3 (aq) = HCO3- (aq) + H+ (aq) 3
CEEGR 342 2013-14: Midterm 2 Name ___________________________
15. A tank holds 250 m3 of wastewater contaminated with 100 mmol/L Ag+. The wastewater also has 10
mmol/L SO42-. We will precipitate the silver (Ag+) down to 25 mmol/L by adding additional sulfate (SO42-).
Calculate the total mass of iron sulfate (Fe2(SO4)3 ; 400 g/mol) required. (15 points) 16. Natural gas is primarily methane (CH4). Calculate the mass of natural gas required to raise the
temperature of a 1-kg iron griddle to 300°C assuming no heat is lost to the surroundings. The initial
temperature of the griddle is 20°C. (12 points)
CH4(g) + O2(g) = CO2(g) + H2O(g) 4
CEEGR 342 2013-14: Midterm 2 Name ___________________________
17. A PFR and CSTR are used in series as shown below. The same 1st order reaction occurs in each
reactor, with k = 0.4/hr. Calculate the concentration of reactant ‘A’ out of the CSTR. Show all work and
steps. (12 points) 5
CEEGR 342 2013-14: Midterm 2

 

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