CHAPTER 15 (energy) – Flashcards
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| energy |
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| the ability to do work the SI unit is the joule (J) or watt usually talked about as something losing energy and something gaining it |
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| US's share of energy |
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| the US has less than 5% the world's population but uses 1/4 of all electricity generated on the planet of that, 33% is used for industry transportation uses 28% private homes use 21% commercial spaces use 17% utilities use 35% to generate electricity |
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| power |
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| the rate at which energy is used the SI unit of power = 1 joule / second |
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| potential energy |
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| energy due to position or arrangement |
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| kinetic energy |
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| energy of motion |
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| energy in the biosphere |
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| 30% of incident radiation from the sun is immediately reflected back into space as short-wave radiation (UV and visible light) around 50% is converted to heat around 23% powers the water cycle .02% is absorbed by plants via photosynthesis, creating the sugars that power the world and replenishing oxygen in the atmosphere |
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| kinetic-molecular theory |
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| describes the effect of temperature on the rates of chemical reactions at high temperatures, molecules move more rapidly and collide more frequently, increasing the chance for reaction increased temperature also provides energy necessary to break chemical bonds concentration of reactants also affects reactions - more molecules in a given space = more likely collisions |
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| thermochemistry |
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| the study of energy changes that occur during chemical reactions (and physical processes) |
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| system |
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| the part of the universe under consideration |
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| surroundings |
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| everything else - the rest of the universe or the parts that exchange energy or matter or both with the system |
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| exothermic |
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| reactions that result in the release of heat from a system to surroundings - chemical energy is converted to heat and absorbed by surroundings energy must be supplied to the reactants from the surroundings |
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| endothermic |
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| energy is absorbed as heat |
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| first law of thermodynamics |
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| energy cannot be created not destroyed - also called the law of conservation of energy |
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| using energy |
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| why do we always need more? - energy can be changed from 1 form to another - not all forms are equally useful - more useful forms of energy are constantly being degraded into less useful forms as energy flows DOWNHILL spontaneously |
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| second law of thermodynamics |
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| the energy available for work in the universe is continuously decreasing (entropy, disorder) when we change energy from one form to another, we can't concentrate all the energy in a particular source to do the job we want it to |
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| entropy |
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| a measure of the dispersal of energy in a system (disorder) the more energy is spread out, the higher the entropy of the system and the less likely it is that this energy can be harnessed to do useful work natural processes tend toward greater entropy or are exothermic or both |
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| microstates |
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| the energy of molecular motion - the number of microstates in which a given sample of matter can exist differs depending on whether it is in the solid, liquid, or gaseous state the number of energy microstates will be lowest for a solid because the molecules in a solid are limited mainly to vibrational motion |
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| fossil fuels |
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| coal, petroleum, natural gas formed over millions of years during Earth's Carboniferous period (300 million years ago) more than 90% of the energy used to support our way of life comes from these fuels of all that ever existed, 90% of fossil fuels have been used up in the last 300 years |
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| fuel |
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| a substance that burns readily with the release of significant amounts of energy - they are REDUCED forms of matter, and the burning process is OXIDATION if an atom already has its maximum number of bonds to oxygen (or other electronegative atoms) the atom cannot serve as a fuel ex of fuels: hydrogen (H2) methane (CH4) carbon (C) glucose (C6H12O6) octane (C8H18) |
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| coal |
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| a complex combination of organic materials that burn and inorganic materials that produce ash C + O2 --> CO2 ranked by coal content: HIGHEST TO LOWEST: anthracite (hard coal), bituminous (soft coal), lignite (brown coal), peat, wood (for comparison) by far the most plentiful fossil fuel solid coal contais materials that are left as ash when coal is burned - some minerals enter the air as PM, a major pollution problem, and SO2 reacts with oxygen and moisture in air to form sulfuric acid when coal is heated in the absence of air a product is left called coke used in the production of iron and steel |
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| natural gas |
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| composed principally of methane, the cleanest of the fossil fuels, burning with a relatively clean flame and mainly CO2 and water as products most likely formed ages ago by heat, pressure, and bacteria on organic matter, trapped in geological formations and removed through drilling methods (and fracking) its principal constituent is methane CH4 |
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| petroleum |
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| complex liquid mixture of organic compounds - hydrocarbons, thought to be of animal origins |
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| obtaining and refining fuels |
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| crude oil is obtained from the ground, must be separated into fractions by boilling and distillation gasoline is usually the fraction of petroleum most in demand - fractions that boil at higher temperatures are often converted to gasoline by CRACKING (converts some molecules to those in gasoline range but also a variety of useful byproducts) the industry can on demand increase the proportion of gasoline in summer or fuel oil in winter from a given supply of petroleum - it can even make gasoline from coal |
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| gasoline |
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| derived from petroleum, a mixture of hydrocarbons gasoline fraction of petroleum as it comes from a distillation column is called straight-run gasoline and doesn't burn very well, but it gets modified |
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| octane ratings |
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| an arbitrary performance standard established in 1927 to show which gasolines burn best some types of hydrocarbons, especially those with branched structures, burn more evenly and are less likely to cause knocking than others isooctane = 100 octane heptane (unbranched) = 0 octane gasoline = 90 octane = same performance as 90% isooctane, 10% heptane octane rating can be improved by heating gasoline in the presence of a catalyst such as sulfuric acid (H2SO4) chemists can combine small hydrocarbon molecules into larger ones more suitable for fuel use - a process called ALKYLATION certain additives substantially improve antiknocking quality of gasoline - ethanol, methanol, tert-butyl alcohol, methyl tert-butyl ether (MTBE) (to replace lead, but not as effective, but must be used in large quantities) oxygenates (various alcohols and derivatives containing oxygen) improve octane rating and decrease amount of CO in auto exhaust |
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| alternative fuels |
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| biodiesel - made from reacting ethanol with vegetable oils and animal fats, can be used in unmodified diesel engines E85 - 85% ethanol, 15% gasoline |
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| electricity |
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| most convenient form (more than liquid or gas) half US electricity comes from coal-burning plants - at best only 40% efficient |
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| coal gasification and liquefaction |
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| gases and liquids are easy to transport, and the process of conversion leaves some of the sulfur and minerals behind, reducing a serious disadvantage of coal as a fuel basic process: reduction of carbon my hydrogen, passing steam over hot charcoal producing synthesis gas (mixture of hydrogen and CO), hydrogen used to reduce carbon in coal or form methane require lots of energy - up to 1/3 of energy content is lost in conversion |
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| nuclear reactor |
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| where nuclear fission is controlled - energy released during fission is used to generate steam, turning a turbine to generate electricity 20% of US electricity comes from nuclear power plants a moderator is used to slow down fission neutrons so they can be absorbed by U-235 atoms (moderators = ordinary water in 75% of the world, graphite in 20%, heavy water D2O in 5%) controlled by control rods made of boron steel or cadmium |
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| advantages of nuclear power |
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| unlike fossil-fuel-burning plants, nuclear power plants produce no CO2 and no SOx or NOx, soot, or fly ash - contributing almost nothing to global warming, air pollution, or acid rain also reduce our dependence on foreign oil sustainable - lots of atoms abundant electricity |
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| disadvantages of nuclear power |
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| expensive to build, expensive to have adequate safety precautions must have emergency back up water to act as coolant to prevent meltdown small probability of serious accident nuclear waste is highly reactive and must be isolated mining uranium produces wastes called tailings, as dust, which can move to surrounding areas thermal pollution is unavoidable - some energy is released as waste heat |
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| Chernobyl |
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| Ukraine, 1986 a reactor core meltdown killed several people outright and 2500 died from radiation, many had to be evacuated |
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| breeder reactor |
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| produces more fuel than it consumes |
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| nuclear fusion |
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| principal fuel is deuterium, and is plentiful, obtained by fractional electrolysis of water problem of radioactive wastes would be minimized - the end product is helium, stable, and biologically inert main problem is temperature must be 100 to 200 million degrees celsius to ignite |
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| solar energy |
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| thinly spread out and difficult to concentrate costly to create photovoltaic cells (silicon) to capture suns rays batteries difficult to manufacture, harmful to environment, don't contain as much energy as should, can't store it over night, not very efficient |
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| biomass |
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| dry plant material, burns very well, and has for centuries emissions are almost entirely water vapor and CO2 the plant initially took in, renewable, powered by the sun but most available land is needed for food production, and only 3% efficiency |
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| hydrogen |
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| produces water and gives off energy when burned gram for gram, hydrogen yields more energy than any other chemical fuel, but most hydrogen is tied up in other molecules, and energy required to break the bonds is more than it gives out |
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| fuel cell |
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| a device in which fuel is oxidized in an electrochemical cell to produce electricity directly the fuel and oxygen are fed continuously - as long as fuel is supplied, current is generated electrodes are made of an inert material that does not react during process about 40-55% efficiency (much more efficient than internal combustion engines) water produced can be used for drinking lighter to store than batteries touch and reliable small possibility of explosion |
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| wind and water as energy |
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| kinetic energy captured by blowing and flowing waterpower provides 7% of electricity production in US, 20% worldwide to obtain more we would have to dam up more rivers, killing ecosystems wind power is 1% of US energy but quickly increasing, but hard to store energy |
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| geothermal energy |
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| using heat of the earth (steady temperature of the earth) to heat and cool homes by using a temperature gradient |
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| ocean energy |
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| difference in temperature of surface of water and depths is high, enough to evaporate a liquid and use vapor to drive a turbine - cycling also harnessing tides rising and falling using mechanisms like waterwheels |
