Day 17 4-11-19.pdf - Chemistry 111 April 11 2019 Announcements • Assignment#9 in class on Tuesday 4/16 • No Class on Thursday 4/18 You will be

Day 17 4-11-19.pdf - Chemistry 111 April 11 2019...

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Chemistry 111 April 11, 2019 Announcements: Assignment #9 in class on Tuesday, 4/16 No Class on Thursday, 4/18. You will be responsible for watching the documentary “Pandora’s Promise” and completing Assignment #10 on your own by Friday, 4/19 at 11:59pm. Exam 4 on Thursday, April 25 th .
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Energy Change of a Reaction Energy in a chemical reaction comes from the difference in the reactant and product bond energies. Bond breaking requires energy and is an endothermic process ( D E > 0) Bond formation releases energy and is an endothermic process. ( D E < 0) Net change represents the energy of the reaction. The difference in energy between the breaking and forming of bonds determines if a reaction will be endothermic or exothermic.
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Fuel is used to create electricity in a power plant: 1. Combustion: 2. Boil water in a closed, high pressure system 3. Turn turbine to create electricity Summary: Energy in a Power Plant Fuel + 2 O 2 (g) CO 2 (g) + 2 H 2 O (l) + ENERGY Environmental Concerns: 1. Byproducts of combustion 2. Warming of cooling water source **Some usable energy is lost as heat to the universe in the process because we are working against the 2 nd Law of Thermodynamics (entropy is decreasing) Potential à kinetic à mechanical à electrical
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No electric power plant can completely convert one type of energy into another Some of the energy is transferred into useless heat (lost to Universe) Net efficiency = electrical energy produced x 100 heat from fuel The higher the temperature of the steam, the more efficient the power plant. Power Plant Efficiency
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Are all fuels created equal? Comparing Different Fuels Fuel + 2 O 2 (g) CO 2 (g) + 2 H 2 O (l) + ENERGY
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History of U.S. Energy Consumption by Source 1776 – 2012
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Coal as a Fuel Coal is a complex mixture of substances. Although not a single compound, coal can be approximated by the chemical formula C 135 H 96 O 9 NS. Contains trace amounts of Si, Na, Ca, Al, Ni, Cu, Zn, As, Pb, Hg. Type of Coal State of Origin % Carbon Energy Content (kJ/g) Anthracite Pennsylvania 85 - 98 30.5 Bituminous Maryland 45 - 85 30.7 Sub-Bituminous Washington 35 - 45 24.0 Lignite (brown coal) North Dakota 25 - 35 16.2 Peat Mississippi 10 - 25 13.0
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Combustion of Coal C 135 H 96 O 9 N S + O 2 à 135 CO 2 + H 2 O + SO 2 + NO x + energy The Good News…. Produces a lot of energy ”Easy” to find The Bad News…. Produces most CO 2 per kJ of heat “Dirty” - produces SO 2 , NO x , PM ( fly ash and bottom ash ) Dangerous and expensive mining Environmental harm Contaminated water supplies (H 2 SO 4 ) Strip mining – stripping away earth and rock to reveal coal underneath
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Coal Use Around the World Despite its drawbacks, many countries (US included) have vast deposits of coal reserves. Coal is still used for much of the fuel around the world.
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Petroleum as Fuel Crude oil (liquid) Yields 40 – 60 % more energy per gram than coal Mixture of many different compounds mainly hydrocarbons (contain C and H) Found within pores of rock formations, such as sandstone, tarry oil sands, and shales Worldwide proven oil reserves
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One of the drawbacks to petroleum is that it must be refined before use.
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