CHEM 106 Prelim 2 Cheat Sheet

CHEM 106 Prelim 2 Cheat Sheet - Chapter 12 Energy and...

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Chapter 12: Energy and Hydrocarbons 3/5 - Energy Units and Magnitudes -Units: 1 “Quad” or quadrillion = 10^15 = BTU, kJ = 10^18 J = 1 exaJoule = 1 EJ, Tera = 10^12 -2005 US Energy Consumption = 100 Quads/yr or 100 EJ/yr or 3.2 TW The Energy Crunch to Come -Prediction is that 27.6 TW of electricity will be needed by 2050, which is more than twice the 13.5 TW we use now -How to attain 27.6 TW by 2050: -Fossil fuels: assume current 12.8 TW -Biomass: 7 TW gain using entire agricultural landmass of the planet to produce biofuels -Wind: 2.1 TW for entire Class 3 landsites -Nuclear: 8 TW with 8000 new reactors -Hydroelectric: 1.5 TW from damming rivers -Basically, its not going to happen -US uses 25% of the world’s electricity – China is close -China building one coal-fired electric plant per week Estimating the Heat of Combustion Average Bond Energies Bond Energy (KJ/Mole) C-H 416 O=O 498 C=O 803 O-H 467 C-C 356 H-H 436 C-O 336 3 Categories: -Energy is consumed overall – sum of the energies required to break bonds in the reactants is greater than energy released by all new bonds formed in the products – endothermic overall (+) – requires energy input, so would not be useful as energy source -Energy is released overall – opposite of last -No net energy change occurs – rare Steps for calculating Heat of Combustion: 1-Break all bonds in reactants (if heat is put in, it’s positive; if heat is given off, its negative) 2-Break all bonds in products 3-Add reactants and products 3/7 - Petroleum -crude oil is refined by heating to 400 C in a still and the vapor goes into a distillation column – more volatile portions of vapors go higher up column – the larger the molecule, the lower its vapor pressure and the less distance it will travel up the column -Incomplete Combustion – knocking or pinging which results in burning a fuel of too low an octane number -Increase Octane rating by: -add branched chain or aromatic compounds -add octane enhancers -Tetraethyl lead – now banned -MTBE – now also banned Coal -Gasification – C + H2O → CO + H2 -CO is a problem 2C +2H2O + Energy → CH4 + CO2 -Liquefaction – liquid fuels are made from coal by reacting the coal with hydrogen gas under high pressure in the presence of catalysts – costs twice as much as normal petroleum Hydrogen -mostly made from coal, therefore producing CO -a cleaner method is to use solar electric to produce H -Heat of Combustion of H2 = -498 kJ Methanol -burns more cleanly than gasoline -formaldehyde is a by-product of combustion of it -methanol has an octane rating of 107 -methanol has half the energy content of gasoline by volume, so larger fuel tanks would be necessary Classes of Hydrocarbons -alkanes – have only C and H for elements -branched alkanes are structural isomers Naming Rules 1. Find the longest hydrocarbon chain 2. Number the carbons in the chain beginning with the end nearest the branching 3. When 2 or more substitutes are identical, indicate by use of the prefixes di-, tri-, tetra- 4. If there are 2 or more different groups, they are listed alphabetically 3/9 – More Shit on Naming of Hydrocarbons
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