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November 30 th, 2007 Chemistry 331 50 minutes Exam 3 Name __________________________________________
Part A : Short answer, 6 points each. Be brief!
- Cathode ½ reactions for different fuel cells are shown below. Identify the fuel cell type.
½ O 2 + 2e -^ Æ O2-^ ________________________________ ½ O 2 + 2e -^ + CO 2 Æ CO 3 2-^ ________________________________ ½ O 2 + 2e -^ + H 2 O Æ 2OH-^ ________________________________ ½ O 2 + 2e -^ + 2H+^ Æ H 2 O ________________________________
- Match Terms on the Left with Descriptions on the Right.
Fusion Heating water by sunlight & circulating to warm a house
+ + + + + + + + + + + + +
- - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - -
Heating fluid by sunlight, using fluid to boil water, make steam, and drive a turbine
Fission Reaction of two nuclei to form one nucleus
Heating by direct sunlight
Solar Thermal Power Separation of 235 U from 238 U
neutron capture by Cd
Passive Solar Reaction of one nucleus to form two nuclei
- Shown below is a picture from a lecture slide.
What device does the picture depict? __________________________
A (^) What is region “A” called? ___________________________________
What has occurred in region A? __________________________________________________
Briefly state how sunlight can cause this device to generate electricity.
0
logC
3 4 5 6 7 8 9 10 pH
Al 3+ AlOH2+^ Al(OH)^2 +
Al(OH) (^30) Al(OH) 4 -
Al (^) TOT
- Match the points in the solubility diagram to the correct description.
Solid is present _____________________
Solid could form by increasing pH ____________________
Solid could form by decreasing pH ___________________ Solid cannot form by adjusting pH ____________________
C A B D
- True or False.
When phytoplankton grows, it consumes O 2 T F Biochemical O 2 demand is usually greater than chemical O 2 demand T F In the process of nitrogen fixation, N 2 is converted to NH 3 or organic N T F Phosphates are more soluble than nitrates, so they wash away faster T F When O 2 is depleted, bacteria will turn to sulfate for energy, then nitrate T F
- When groundwater is contaminated, monitoring wells are used to follow the concentration of the flowing contaminants. In the space given below, sketch two curves illustrating the concentration vs time profile for (a) a contaminant that doesn’t bind to soil, and (b) a contaminant that binds to soil. Using points from these curves, finish the equation that defines the retardation factor.
Concentration R = __________
Time
- What does TSCA stand for? What is significant about this piece of legislation in terms of how it has changed environmental chemistry?
- (18 points) Calculate the amount of energy available from the reaction shown below in kJ per mole of 2 H reacted. Use the following masses: 2 H (2.01410 amu), 3 H (3.01605 amu), (^4) He (4.00150 amu), 1 n (1.00866 amu).
21 H + 31 H → 42 He+ 01 n
EXTRA CREDIT (10 points)
Assume you had a two-phase system consisting of just soil and air and you wanted to solve the equilibrium partitioning problem involving,
POP(soil) Æ POP(air)
Show how you could find the equilibrium constant for this if all you had available were K (^) d and H.
Possibly Useful Information E = mc 2 ln(C (^) t / C 0 ) = -kt t (^) ½ = 0.693 / k Kd = Cs / Cw K (^) oc = Coc / Cw f (^) oc = moc / msoil Kow = Co / C (^) w H = Pair / C (^) w PV = nRT f (^) aq = n (^) w / n (^) tot c = 3.00 x 10 8 m s -1^ R = 0.0821 L atm mol -1^ K- Reaction of “NOM” with dichromate: 3CH 2 O + 2Cr 2 O 7 2-^ + 16H+^ Æ 3CO 2 + 8H 2 O + 4Cr3+ Reaction of “NOM” with oxygen: CH 2 O + O 2 Æ CO 2 + H 2 O
Sign here to acknowledge that you have abided by the UMW Honor Code in taking this exam. Signature ______________________________________
