CH217 Final 2013 Physical Constants



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CH217 Final

2013
Physical Constants:

Speed of Light (c) 2.9979 x 108 m/s Plank’s Constant (h) 6.6262 x 10-34 j/s

Faraday Constant (F) 9.6485 x 104 C/mol Gas Constant (R) 8.314 j/mol K

Avogadro’s Number 6.02x1023 Gas Constant (R) 0.0821 L Atm./mol K




  1. Why is the average surface temperature of the earth 288K? How does this compare with the temperature of the moon?

The temperature of the earth and the moon is determined by the steady state heat balance between incoming UV/Vis solar radiation and outgoing IR radiation. This is controlled by the sum-earth distance, and the composition of the earth surface and atmosphere. The composition of the atmosphere is strongly influenced by the Earth’s size which influences gravity. On the Earth the surface temperature is warmer due to greenhouse gases that trap IR light and effectively keep a layer of warm air near the surface. The moon has very little atmosphere and as a result has a much colder average temperature and much greater swings in temperature from day to night.




  1. Freon, CFC-22, is building up in the atmosphere at a rate of 2.6 %/year. If the current concentration of CFC-22 is 119 pptv (parts per trillion by volume), what is the net molar flux of CFC-22 to the atmosphere? The atmosphere has 2.0 x 1020 moles of gas.




Mass of Atmosphere

2.00E+20

moles




CFC-22




119

pptv

since PV=nRT, volume ratios are equivalent to mole ratios

CFC-22




2.38E+10

moles




change




2.6%

percent




Flux




6.19E+08

moles/year






  1. John Martin, a Colby Biology major class of 1955, was the first scientist to publicly propose adding iron to the ocean to modify global climate. His famous quote at a Woods Hole conference, “Give me a half tanker of iron, and I will give you an ice age.” Touched off a national debate on engineering the oceans to control climate.

Martin proposed that iron, like phosphorus and nitrogen, is a necessary nutrient for all plants. Plants have an iron to carbon mole ratio of 0.001 to 106. Because iron is very insoluble, it can be in very short supply in large areas of the ocean. Indeed, when Martin added iron to samples of ocean water he did observe increased phytoplankton growth.


  1. How could adding iron to the ocean influence global temperature? Draw a diagram showing the most important processes and support your drawing with a focused essay.

106 CO2 + 0.001 Fe + 1 PO4 + 16 NO3 + 122 H2O--> Biomass + 138 O2


If Fe is limiting the addition of iron will increase the rate of photosynthesis and “fix” more CO2 in the surface ocean to biomass. This biomass will sink and remove carbon from the surface ocean. CO2 from the atmosphere will exchange across the air/sea interface to replace the missing CO2. In this way Fe helps to drive the biological pump transferring CO2 from the atmosphere to the deep ocean.


  1. How would the addition of iron described in this problem qualitatively change the pH, total CO2, and alkalinity of the surface ocean? Assume biological processes occur on a time scale of days and vertical mixing occurs on a time scale of a week. Please justify each answer with a one-sentence explanation.


If biological processes are faster than gas exchange then the growth of phytoplankton will decrease surface CO2, decrease total CO2, but will not change the alkalinity (no significant change in charge). Under conditions of decreasing CO2 and constant alkalinity the pH will increase.


  1. How would the surface ocean concentration of CO2 and O2 change in part b under really low wind and really high wind conditions?

Under high wind the gas exchange rate will increase and the CO2 will reach close to equilibrium values with the atmosphere. The CO2 will increase compared to part B. Oxygen, a product of photosynthesis will decrease toward equilibrium with the atmosphere. Low wind conditions will reduce gas exchange rates resulting in lower CO2 and higher O2.




  1. The concentration of oxygen in Snow Pond this past Friday was 11.3 ppm. What is the molar concentration of oxygen in the lake and would you expect oxygen to increase or decrease in the surface of the lake over the next month? What about the oxygen concentration in the deep water of the lake? Explain.




Oxygen

11.3

ppm




11.3

mg/L




1.13E-02

g/L

O2

32

g/mole




3.53E-04

mole/L




3.53E+02

uM

The oxygen concentration in the surface of the lake will oscillate every day due to photosynthesis and respiration, but the month long trend will be deceasing dissolved O2 due to warming of the water.

The oxygen concentration in the deep water will be constant on the short term because diural cycles in productivity doesn’t occur. The temperature is constant so deep O2 might be expected to be constant, but in reality respiration will consume significant amounts of O2.


Please read the following letter that was published in Environmental Science and Technology this month.

Keystone XL: Pipeline to Nowhere

Use of coal, oil, and natural gas has to stop (in that order). But “dirty” oil, emanating from oil sands (a.k.a., tar sands) with a significantly higher carbon footprint than conventional oil, deserves a place at the front of the line. The proposed Keystone XL pipeline would enable development of oil sands from Alberta, Canada, to the U.S., but this dog will not hunt. It is a pipeline to nowherea dead end in our economic future.

The fossil fuel age is coming to a close and only those fuels with the least carbon content should be used. Fossil fuels are linked to an exponential build-up of greenhouse gases in the atmosphere and an increasing frequency of extreme events floods, droughts, wildfires, and storms. Unless we wish to see more events like the 2003 European heat wave, the 2010 drought and wildfires in Russia, and 2012 Superstorm Sandy; we should begin to phase-out carbon-laden fuels. Denying the construction of the Keystone XL could be a resolute signal that President Obama is serious about climate change.

A portion of the Keystone Pipeline is already reality  it runs from Hardisty, Alberta to Steele City, Nebraska, and two branches then extend to Patoka, Illinois and Cushing, Oklahoma. Do we really need a parallel extension to transport an additional 830000 barrels/day of crude to refineries in the Gulf Coast? After all, the U.S. became a net exporter of refined petroleum products in 2008, so most of it would be exported anyway.

Here’s the case against the Keystone XL:


  1. We do not really need the oil. Energy efficiency is actually the key(stone) we should be focusing on. With new EPA regulations on light duty vehicles coming online now through 2025, the savings from fuel efficiency alone will account for 2 million barrels/day, more than twice the oil that would flow from Keystone XL. Consumers will save $3,400−$5,000 in net fuel costs over the lifetime of their vehicle from these new rules; and 2 billion metric tons of greenhouse gases will be avoided. Clearly, energy efficiency trumps fossil fuel development in every way.

  2. Keystone XL would add to global greenhouse gas emissions. New infrastructure like Keystone XL will increase demand and the rate of development of Alberta oil sandsoil with a very large carbon footprint (17% higher than crude oil produced in the U.S.) according to the recent Draft Supplemental Environmental Impact Statement by the U.S. State Department. It is true that burning an additional 830 000 barrels of oil per day does not represent a large fraction of total greenhouse gas emissions worldwide, but it is a step in the wrong direction.

  3. It is a slippery (and oily) slope. If XL is approved, the deposits of oil sands potentially available for development in Alberta are truly massive, 170 billion barrels of oil, enough to raise the carbon dioxide concentration of the entire atmosphere by almost 10 ppm if it was completely extracted and burned.

  4. Let Canadians decide. Pipeline proponents say that China will buy the oil anyway if the U.S. does not. That may be true. But if Canada is to develop the oil sands for sale to China, from two to six million barrels per day as planned, it would require new pipelines across Alberta and British Columbia through sensitive ecological regions and first nation’s property. The proper place for such a decision is with Canadians and first nations.

  5. When do we start to stop? If not now, when? It has been a good run, this fossil fuel age. But from the invention of steam power in the 1700s when industrial society first started to burn huge quantities of coal, the future was preordained. One cannot burn all the fossil fuels that required 300 million years to form in just a few centuries and not expect to pay consequences. The fossil fuel age has massively disrupted the balance of oxidation and reduction on earth. Thus, elemental cycles yield more oxidized products like acid rain (nitric acid, sulfuric acid) and carbon dioxide as a result.

For all these reasons, we do not need a pipeline without a future. It is a pipeline to nowhere. Jerald L. Schnoor, Editor-in-Chief, ES&T

5) Please answer the following questions related to the letter.



  1. Based on what you know about other hydrocarbons, what is it about the chemical composition of the tar sands oil that results in a 17% greater carbon footprint?

XL oil has a larger C:H ratio resulting in more CO2 produced per unit of energy.

  1. Biomass also has a large carbon footprint, what makes biomass a preferred (better) fuel source?

Biomass is produced by contemporary plant growth that should sequester as much CO2 during growth as is released during combustion.

  1. In point 5, Schnoor describes a massively disrupted balance of oxidation/reduction (redox) on earth. What are the redox reactions that he is describing and how have these reactions powered our industrial society since 1700. Where has the energy come from?

The oxidation is the conversion of reduced carbon (CH4) to oxidized carbon (CO2).

The reduction is the conversion of O2 to H2O and CO2.

Other redox reactions include the oxidation of sulfer (s) to SO2 and H2SO4, and N2 to NO, NO2, and HNO3.

These redox reactions are the source of energy in the combustion of hydrocarbons. They allowed large-scale industrial development through the availability of cheep, abundant power.

The source of hydrocarbons is photosynthesis driven by solar energy collected by plants over the last 500 million years. (the reverse of the redox reactions listed above).



  1. In point 1, why is Schnoor focusing on energy efficiency instead of other renewable energy sources like wind or solar? Do you agree with this argument?

The best source of renewable energy is the energy that you do not have to produce. Conservation reduces the energy requirement for the society and makes it possible to meet the remaining energy demand with smaller installations of alternative energy systems.


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