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September 29 th, 2007 Chemistry 331 50 minutes Exam 1 KEY
Possibly Useful Information
t (^) res = C / F P = P 0 e -(MW x gh / RT)^ PV = nRT Efficiency < 1 – (T (^) c / T (^) h) R = 0.0821 L atm mol -1^ K-1^ OR 8.314 J mol-1^ K-
Part A : Short answer, 8 points each. Six sentences or less!
- Match the items on the left to the most appropriate term on the right.
Coal gasification
Respiration
Fluidized bed combustion
Primary energy use
Photosynthesis
Fractional distillation
Cracking
Endothermic
Making gasoline by heating higher boiling fractions in the absence of air
Reacting coal with hot steam to make methane
The biological conversion of organic carbon to CO (^2)
Energy obtained directly from a fuel source Enhanced recovery
- What is tar sand? How is fuel obtained from it?
This is sand loaded with an oily (fossil fuel) substance called bitumen. It is either excavated and extracted with steam or it is softened in the ground by steam injection and then pumped out. After extraction, it is subjected to fractional distillation.
- Explain how gas influx into the atmosphere can be a zero-order chemical process.
A zero-order chemical process is one whose rate does not depend on the concentration of any chemical species. Gas influx to the atmosphere from human sources is not dependent on the atmospheric concentration of the gas but rather the rate at which we use energy.
- Briefly describe the main elements of the steady-state model for earth’s temperature with explicit reference to the solar flux, albedo, and the wavelengths of radiation involved in the energy balance.
The model equates the solar energy absorbed by the earth with the energy emitted by the earth (i.e., no net energy gain). The solar flux is the energy radiated through space by the sun, and it is mainly UV and visible wavelengths. Some portion of it is intercepted by earth. About 30% of that is reflected due to earth’s albedo. The earth warms and emits heat. The wavelengths it emits depend on temperature and are mainly in the IR.
- What factors determine how much radiative forcing a gas will introduce to the atmosphere?
How much of it is being put into the atmosphere; what its residence time is; how strongly it absorbs thermal IR radiation; whether the radiation it absorbs lies in the atmospheric
window (7 and 14 μm).
Part B : Calculate this! 20 points each. Show all work.
- Use the bond energies on the last page of this exam to calculate the moles of CO 2 produced per 1000 kJ when one mole of ethanol (CH 3 -CH 2 OH) is combusted completely to CO 2 and H 2 O.
CH 3 CH 2 OH + 3O 2 Æ 2CO 2 + 3H 2 O
Bonds broken: 1DC-C + 5D (^) C-H + 1DC-O + 1DO-H + 3DO=O (347) + 5(410) + (360) + (460) + 3(494) = 4,699 kJ Bonds formed: 4DC=O + 6D (^) O-H 4(799) + 6(460) = 5,956 kJ Enthalpy: (4,699 - 5,956) = -1257 kJ
So, [(2 mol CO 2 ) / 1257 kJ] x 1000 = 1.59 mol CO 2 per 1,000 kJ
