# Critical Thinking Exam about Population and Energy Production

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Ch 371

Critical Thinking Exam about Population and Energy Production

Due May 5, 2008
You may work with one other person in the class to do any of the necessary mathematics. All of your mathematical answers must be worked out in detail on this examination. If you are rusty with working math problems, you can find a review of how to work such problems at http://www.chem.tamu.edu/class/fyp/mathrev/mr-da.html . All opinions expressed on this exam should be your own and not those of others in the class! You must indicate who your teammate is if you have one. Any opinions that you express on this exam must be typed although you may write out your calculations by hand.

1. (4 pts) How long will it take for a mice population to double if it is growing at a rate of 5%?

1. (20 pts) You have been given a job as a resource manager for the State of Oregon, and you need to examine the population base as a function of county within the state. This is your first day on the job, and your boss asks you to answer the following questions using the Oregon Population Statistics provided. What would be the projected population of Polk County in the year 2010?

2. What is the fastest growing county (in terms of percentage not raw population) in Oregon since 1960?

3. Where are the regions of fastest and slowest growth in Oregon?

4. Compare the growth rates from 1970 to 1980 with those from 1980 to 1990 for Polk and Marion Counties. What do you see and do you have an explanation for this result? That is, was the growth rate the same between decades, higher or lower?

5. Using your knowledge of exponential growth, determine the average growth rates from 1950-1995 for the following counties: Deschutes, Jackson, Lane, Lincoln, Marion and Multnomah. Are these the kind of growth statistics you would have predicted for each of these counties? Why or why not.

Some of the following questions are intended to make you think about how to make choices concerning the production and use of energy.

1. (6 pts) Joe Sixpack lives in the desert with a solar powered beer cooler. On average, 800 watts per square meter of solar energy are present at Joe's location. Over an 8 hour period, Joe requires 2.5 KWH of energy to keep his beer cold. Joe's PV panels are 10% efficient. Approximately how many square meters of panel does Joe require? Is this a good way for Joe to cool his liquid refreshments?

1. (6 pts) About 20% of the electrical energy we consume is used for lighting. A 15 W fluorescent light bulb produces as much light as a 75 W incandescent light bulb. The fluorescent bulb has a life expectancy of 10,000 hours while an incandescent bulb lasts about 1000 hours. The fluorescent bulb costs \$20 (why no one buys them) while the incandescent bulb costs about \$0.75 (why everyone buys them). Assuming that electricity costs \$0.10 per KWH, compare the cost of using a fluorescent bulb to the cost of the incandescent bulb. Which should you use if you are interested in saving energy and money?

1. (6 pts) Describe in detail how a crystal of silicon, normally a non-conductive material, can be transformed into a material capable of carrying a current.

6. (9 pts) Strontium-90 is a nuclide that is present in the radioactive fallout from nuclear weapon explosions. Sr-90 decays via a beta emission and has a half-life of 28.0 years.

a. Write a balanced equation for the decay process.
b. How long will it take for 94% (15/16) of the Sr-90 atoms in a 1 gram sample to undergo decay?
c. Look at strontium's position on the periodic table. Do you think that presence of this isotope in the environment presents a hazard? Why or why not? Does this information influence your views on nuclear weapons?

1. (6 pts) Consider the U-238 decay series scheme attached to this exam. Which of the decay products are likely to be most abundant in a soil rich in uranium? Why? What are the health risks of these isotopes?

1. (4 pts) There are approximately 120 nuclear power reactors in the U.S which account for about 22% of our total domestic electrical production. Over a 30 year lifecycle, each plant requires about 5000 tons of uranium. It is estimated that the U.S. possesses about 2.5 million tons of recoverable uranium. At current usage, how long will U.S. uranium resources last?

1. (10 pts) The major component in natural gas is methane, CH4 while the bottled gas used in your gas barbecue is propane, C3H8. If each of these gases burns completely, compare the amount of energy released by each material in terms of (a) kJ.mole of CO2 produced and (b)kJ/g of fuel. Do these calculations based on the breaking and forming of bonds during the combustion reaction. You will find the bond energies you need in Table 2.1at the end of this exam. The balanced equations for the two combustions are given below.

10. (6 pts) You are contemplating purchasing a small vehicle for your daily transportation needs. Decide whether it would be economically more practical for you to use a gasoline powered vehicle or an electrically powered one. Assume that electricity costs \$0.06 per kWh while gasoline in Monmouth costs \$2.00 per gal. Gasoline weighs 5.51 lb/gal and upon combustion releases 19,000 BTU per pound.

Energy units: 1 calorie = 4.18 j = 1.16 x 10-6 kWh = 3.97 x 10-3 BTU
a. If an electric engine is 50-80% efficient and a gas engine is 20-25% efficient, which is going to be more economical for you to use based on fuel costs? To answer this you will want to compare the costs per unit for using electricity and gasoline.
b. How would the fuel source used by your electric utility for producing electricity influence your choice of vehicle? Consider an electric utility that uses geothermal power, one that uses coal and one that uses nuclear fuel. Demonstrate your critical thinking skills here.

11. (8 pts) The amount of energy required to produce disposable consumer goods is an important environmental issue. In this problem you will explore the energy issues surrounding the use of paper versus polystyrene as material for making disposable coffee cups.

The facts:

It takes 980 kWh of power to produce a metric ton of paper.

It takes 300 kWh of power to produce a metric ton of polystyrene.

A paper cup that holds 8 oz. of coffee weighs 10.1 g.

A polystyrene cup that holds 8 oz. of coffee weighs 1.5 g.

1. Compare the amount of energy expended in making a paper cup and a polystyrene cup.

2. Both types of cups can be incinerated (a combustion reaction like that of fossil fuels) to generate heat energy. A paper cup yields 20 Mj/kg (megajoule per kilogram) and a polystyrene cup 40 Mj/kg. This heat energy can be converted to electricity at a powerplant with an efficiency of about 30%. Compare the amount of electrical power available from incinerating discarded paper and polystyrene cups with the amount of energy needed to produce them. (1 kWh - 3.6 x 106 joules).

3. A fast-food restaurant on a busy street uses 2.5 gross of polystyrene coffee cups per day (1 gross = 12 dozen = 144). Reacting to pressure from an environmental advocacy group, the restaurant switched to using paper cups. What is the effect of this decision in terms of kWh of power per week, if the town has no incinerator? What is the effect if the town sorts and incinerates paper and plastic for electricity production?

4. *Write a paragraph explaining to the proprietors of the restaurant in question (c) what they might do if they want to be as environmentally responsible as possible.

12. (5 pts) You may need to do a bit of research to answer this question. Consider the accident at Three Mile Island and when it occurred. Find out what the movie The China Syndrome was about, and when it was released. Is here a connection between these events, and public perception of nuclear safety?

13. (10 pts) There are several ways in which you can combat the carbon dioxide you produce by driving your car and using electricity.
(i) Describe how these green tags work
(ii) How much would you need to spend to offset the carbon dioxide you would produce by driving 12,500 miles a year in a car that gets 15, 20 and 30 miles per gallon.
(b) Go to http://www.treesforlife.org.uk/tfl.global_warming.html to learn about the tree alternative.
(i) Explain how trees offset carbon dioxide production.
(ii) How many trees would you need to plant to off set the carbon dioxide that you estimate you will produce over the next year?

SOME AVERAGE BOND DISSOCIATION ENERGIES

 Bond Enthalpy (kJ/mol) Bond Enthalpy (kJ/mol) H-H 432 C=O 1,071 O=O 494 C-C 347 O-H 460 C=C (non-aromatic) 611 C-H 410 C=C (aromatic) 519 C-O 360 N=O 623 C=O 799 NΞN 941

Oregon Population Statistics
County 2000 1995 1990 1980 1970 1960 1950
Baker 16741 16471 15317 16134 14919 17295 16175

Benton 78153 75235 70811 68211 53776 39165 31570

Clackamas 338391 316428 278850 241919 166088 113038 86716

Clatsop 35630 35372 33301 32489 28473 27380 30776

Columbia 43560 41816 37557 35646 28790 22379 22967

Coos 62779 62822 60273 64047 56515 54955 42265

Crook 19182 16386 14111 13091 9985 9430 8991

Curry 21137 21243 19327 16992 13006 13983 6048

Deschutes 115367 94974 74958 62142 30442 23100 21812

Douglas 100399 99906 94649 93748 71743 68458 54549

Gilliam 1915 1861 1717 2057 2342 3069 2817

Grant 7935 7976 7853 8210 6996 7726 8329

Harney 7609 7075 7060 8314 7215 6744 6113

Hood River 20411 18589 16903 15835 13187 13395 12749

Jackson 181269 166060 146389 132456 94533 73962 58510

Jefferson 19009 15969 13676 11599 8548 7130 5536

Josephine 75726 71335 62649 58855 35746 29917 26452

Klamath 63775 61043 57702 59117 50021 47475 42150

Lake 7422 7421 7186 7532 6343 7158 6649

Lane 322959 303426 282912 275226 213358 162890 125776

Lincoln 44479 44347 38889 35264 25755 24635 21308

Linn 103069 100130 91227 89495 71914 58867 54317

Malheur 31615 27860 26038 26896 23169 22764 23223

Marion 284834 255044 228483 204692 151309 120888 101401

Morrow 10995 8922 7625 7519 4465 4871 4783

Multnomah 660,486 614104 583887 562640 556667 522813 471537

Polk 62380 56678 49541 45203 35349 26523 26317

Sherman 1934 1886 1918 2172 2139 2446 2271

Tillamook 24262 23767 21570 21164 17930 18955 18606

Umatilla 70548 64040 59249 58861 44923 44352 41703

Union 24530 24948 23598 23921 19377 18180 17962

Wallowa 7226 7535 6911 7273 6247 7102 7264

Wasco 23791 22737 21683 21732 20133 20205 15552

Washington 445342 370197 311554 245808 157920 92237 61269

Wheeler 1547 1539 1396 1513 1849 2722 3313

Yamhill 84992 75443 65551 55332 40213 32478 33484

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