chapter 14: energy: a fuels paradise chemistry for changing times 10 th edition hill/kolb daniel...
TRANSCRIPT
Chapter 14: Energy: A Fuels Paradise
Chemistry for Changing Times 10th editionHill/Kolb
Daniel Fraser
University of Toledo, Toledo OH
©2004 Prentice Hall
Chapter 14 2
Energy
• Ability to do work– Move car– Move electrons through copper wire
• Abundant energy is basis of modern civilization
• Convert raw materials to finished products
Chapter 14 4
Types of Energy
• Potential energy: energy due to position or arrangement
• Kinetic energy: energy of motion
Chapter 14 5
Energy Transferred in Chemical Reactions
• Exothermic reactions: release heat to environment
• Endothermic reactions: gain heat from environment
Chapter 14 6
First Law of Thermodynamics
• Also called law of conservation of energy
• Energy can be neither created or destroyed; it can only change forms
• Means: cannot have a machine produce more energy than it consumes– We can’t “win”
Chapter 14 7
Second Law of Thermodynamics• Entropy: amount of
disorder in a system
• Second Law states that entropy is always increasing– Universe becoming
more disordered– Need energy to put
things in order
Chapter 14 8
Early Fuels
• Human power
• Animal power– Domestication of horse and oxen
• Wood– Still used in many places as primary fuel
• Waterpower– Direct use good only for small scale factories
Chapter 14 9
Fossil Fuels
• Coal, petroleum, and natural gas
• Produce ~90% of energy
• Release significant amounts of heat when burned
• Reduced forms of matter
Chapter 14 10
Rate of Usage of Fossil Fuels• Nonrenewable source of energy
• Using about 50,000 times faster than can be replenished
Chapter 14 11
Coal• Complex combination of organic and inorganic
materials– Formed from ancient plant material
• Quality of coal depends on carbon content
• Most plentiful fossil fuel
Chapter 14 12
Coal Gasification and Liquefaction
• Convert coal to more usable forms
• Leaves behind most of the impurities
• Requires lots of energy and water
• Dispose of materials left over
Chapter 14 13
Uses and Problems of Coal
• Very high energy released when burned• Source of organic chemicals• Coal mining is one of the most dangerous
professions• Source of pollution
– Fly ash– American coal has high sulfur content– Need to clean it before burning
Chapter 14 14
Natural Gas
• Mostly methane, CH4
• Mostly used as fuel
• Used as raw material for industry– Used to make starting materials for plastics
• Rarest of the fossil fuels
Chapter 14 15
Petroleum
• Complicated mixture of liquid organic compounds– Mostly hydrocarbons– Probably produced from ancient animal material
• Used for fuel and raw material
• Source of most industrial chemicals
Chapter 14 18
Gasoline
• Mixture of C5H12 to C12H26 hydrocarbons
• Some of these hydrocarbons are better fuels– The more branched, the better
• Octane rating– Isooctane assigned value = 100– Heptane assigned value = 0
• Octane rating = 90 means the same as having 90% isooctane and 10% heptane
Chapter 14 19
Gasoline Additives• Used to improve octane rating• Tetraethyl lead is most effective
– Lead contributes to learning disabilities in children
• Methyl tert-butyl ether (MTBE) – – Improves octane rating– Lowers CO emission– Toxic if it gets into groundwater
• Ethanol– Produced by fermentation of corn– Favored in farm regions
Chapter 14 20
Electricity
• Most convenient form of energy
• Any fuel that can boil water can be used to produce electricity
Chapter 14 21
Nuclear Energy
• Nuclear reactors use nuclear fission– Heat released is used to boil water
• Widely used– France gets >75% of electricity from nuclear energy
• Does not use fossil fuels
• No air pollution
Chapter 14 22
Nuclear Problems
• Must shield workers from radioactivity
• Prevent contamination if a problem arises
• Disposal of wastes– Some waste products have half-lives of
thousands of years– Hard to build site that lasts that long
Chapter 14 23
Nuclear Fusion• Process used by the sun
• Use 2H as fuel– Rare but have oceans of water to use
• Great technical difficulties have yet to be overcome
Chapter 14 26
Uses of Solar Energy
• Only about 10% of sunlight is converted to electricity
• Solar cells tend to be expensive– Price is coming down
• What do you do on cloudy days?
Chapter 14 27
Biomass
• Use plant material as energy source
• Can use directly – Burn material
• Can convert to another form– Make alcohol from grains– Produce methane from breakdown of plant material
• Not very efficient way to produce energy
Chapter 14 28
Hydrogen
• Burns very cleanly
• Chemically tied up in other compounds– Requires energy to separate from water
• Hard to store
• May be used in fuel cells
Chapter 14 29
Fuel Cell• Fuel oxidized in an
electrochemical cell
• Requires fuel and oxygen be continuously provided
• Produces electricity– 40–55% chemical
energy converted