September 28

Chapter 4-- Energy and Etc.

Background-- energy is conserved (remains)

• but changes forms
• mechanical
  • kinetic (motion)
  • stored (as a spring, water behind a tall dam)
• electrical
• light
• heat
  • power plants change heat to electrical energy
  • lamps change electrical energy to light, heat
  • motors-- change electricity to motion
• chemical
  • two way street
  • some species seem to store energy
    • reaction (like burning) releases heat
    • most of the chapter focuses on fuels
  • other species need energy to change
    • heat can change CaCO₃ into CaO + CO₂
    • Al⁺³ + lots of electricity ---> Al metal

Ultimately, all energy is nuclear

• what fires the sun and stars
• powered the Big Bang (origin of the universe)
• provides much of the earth's internal heat
• at much tinier level-- our nuclear power

Not a useful approach

• may be more reasonable to say most of what we know is due to sunlight
  • sunlight produced the fossil fuels
  • sunlight causes wind, water movement
  • sunlight drives all agriculture
• but even this isn't that useful--

Easier to treat fuels as stored energy--

• chemical energy
  • trace the origins if you want
  • but treat as a source of energy

HEAT is perhaps the most recognizable form of energy

• evaluated by ability to make objects warmer
  • 1 calorie = heat needed to make 1 g of water change temperature by 1^oC

• To heat 500 ml (pint) of water to boiling?
  • 20^o to 100^o C= DT= 80^o
  • mass = 500 grams
    • (water: 1 ml=1gram)
  • need 80x500 = 40,000 calories
  • or 40 kilocalories
    • 1 kcal also called 1 (big-C) Calorie
    • (big-Calorie is the unit for food)
  • in SI 1 cal = 4.184 Joules
• so we need 40 x 4.184 kJ of energy= 167 kJ

• A little more units/arithmetic
  • 1 watt = 1 Joule per second
  • a small microwave has 860 Watt output
  • 167000 J (needed) / 860 (J/sec) = 194 sec
    • that's about right (3 minutes)

The reaction of glucose + O₂ --> CO₂ + H₂O

• produces heat
• if we burn the sugar
• if we eat, metabolize the sugar
  • heat is the same
  • depends only on net process
  • not on the manner of change
    • (useful-- simplifies tables we use)
• easier to measure if we burn it
  • example: peanuts

Themes of Chapter

• understand how to work with chemical energy
  • measure it
  • store that information
  • retrieve and use the information
• look at major sources (fuels mainly)
  • what are they (coal, petroleum)
  • how are they used
• look at alternatives, including conservation
  • (chapter largely ignores storing energy chemically or using it chemically)

Look first at a fire

• Many materials can be mixed without reacting
  • But can be made to react
  • Need to start the reaction
    • light paper with a match
    • spark plug ignites gas vapor
    • detonator reaction sets off explosive
• Reactants need energy to start the reaction
  • called Activation Energy
  • one source: heat the materials
• Molecules that get that energy can react
  • they may give off heat as they react
  • this can heat nearby materials
  • can keep a flame lit or cause faster explosion
• Some reactions get the energy from light
  • UV curing glues

Brief, simplified description of hydrocarbons

• Hydro=H + Carbon = C
• simplest is CH₄

• C almost always forms four bonds
  • has four valance electrons, seeks 8
  • gets and shares 4 more electrons
    • could include double bonds
• H generally forms 1 bond

• Interesting-- C to C bonds
  • provides backbone of many compounds
  • C-C eth.. (ethane, ethanol)
  • C-C-C prop... Propane is C₃H₈
  • C-C-C-C but... Butane is C₄H₁₀
    • includes variations like... (branched-- Web won't draw this well)
  • C5 = pent...
  • C6 = hex...
  • C7 = hept
  • C8 = oct... Octane is C₈H₁₈

Petroleum is a complex mixture

• mostly hydrocarbons
• varies from C₁ to perhaps C_20-30
• black liquid-- thin to thick to tar

• Distill -- heat
  • smaller molecules ---> gases or vapors
  • cool and collect vapor (condense)
  • fractional distillation
  • can separate the mixture
• C1 - C4 are gases at room temperature
  • separate easily
• C3 and C4 stored under pressure, tanks
• C5-C12 solvents, evaporate
  • good fuel for cars (gasoline)
  • thin fluid (easy to pump)
  • evaporates quickly
  • burns quickly then
  • reaction is exothermic
    • produces heat
    • directly produce mecanical work
• C12-C15 still are liquids
  • found in diesel and jet fuels
• C15-20 more viscous (pour slowly)
  • lubricating oils
• larger = solids:
  • asphalt, waxes, paraffin

NW Ohio and Petroleum

• This region-- BG to about 25 miles south
  • Cygnet, Findlay, North Baltimore
  • large homes, West Wooster = oil money
  • was worlds largest active petroleum site
    • late 1880's for about 15-20 years
    • boom town / then bust
    • died as Texas Spindle Top opened
  • also was major natural gas source
    • BG, Toledo, Findlay
    • promoted clean, free fuel
    • lured Glass industry from New England

Modern refinery--

• can break down larger molecules
• can reassemble
• can decide on output mixture
  • gasoline in summer
  • more fuel oil in winter
    • less gasoline and asphalt

• also a great chemical Lego Set
• Petrochemical Industry
  • can build other molecules
  • tear apart and rearrange
  • alcohol, antifreeze, polymers
    • plastics, fibers, films

Petroleum-- Overall picture

• need to discuss sources and ownership
• international politics
• local politics
• national policies and incentives
  • seldom noted, but example where free market forces and competition really no longer exists in usual sense
• existing technology inhibits alternatives
  • self interest
  • existing infrastructure = no new expenses

• Other Fuels
  • Natural Gas-- methane
    • (swamp gas, from decay in landfills)
  • Hydrogen
    • can make from water (electrically)
    • then no net energy gain
    • may still make sense
      • can make H₂ with off-hour electricity H₂ is very clean fuel
      • is renewable, chemically
  • Ethanol (alcohol)
    • cheapest source-- petroleum
    • more costly-- ferment corn, molasses
    • slightly cheaper-- ferment crop wastes
    • renewable-- maybe
      • chemically yest
      • energetically questionable

Demos

• delayed reaction
  • two reactions Na₂O₂ + H₂O --> NaOH + O₂ + heat
  • once hot Al + Na₂O₂ -- > Al₂O₃ + Na₂O = lots of heat
• catalyst
  • H₂O₂ and catalyst (KMnO₄ or Yeast)
  • H₂O₂ (usually stable) ----> H₂O + O₂
    • bubbles
    • soap = stable foam
• calories
  • burn peanuts (mostly oil)
  • Al can with water
  • Digital thermometer

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