 Ancient Fuel Source
 Sunlight
 Plants captured and stored the energy from the sun via photosynthesis
 Via molecule called chlorophyll
 6CO2 + 6H2O + 2800 kJ C8H12O
 Decay of plants usually goes to CO2 and water, but sometimes, under certain conditions, get
 “vegetable matter” That was transmuted over millions of years into fossil fuels:
 Coal and petroleum
 Coal
 Most plentiful fossil fuel
 Us estimated to have more than 40A% of the world’s coal reserves of coal
 Us electric utilities burn nearly 700 million tons of coal each year
 55% of total
 Disadvantages
 Difficult to obtain, mining dangers
 Strip mining requires replacement of earth, topsoil, and vegetation
Transportation of coal requires energy
 A possible future
 Instead of burning, use as a source of carbon, C, in alternate fuel
 Petroleum
 Mixture of hydrocarbons
 A hydrocarbon is a molecule made of C and H
 Must separate these different molecules before using them
 Distillation
Higher melting point
Distillation
Separation process
A solution is heated to its boiling point and the vapors (gases) are condensed and collected
Fractional Distillation
Heat crude oil
Vaporizes
Temperature gradient in tower
Coller on top, away from heat source
Lighter molecules with lower boiling points vaporaze and lower temperatures, rise to top, coll,
condense
Crude oil: uses
42 gallons in a barrel of il
35 gallons for heating and transportation
7 gallons for non-fuel uses
1.5 gallons for “feedstocks”, reactants for pharmaceuticals, plastics, fabrics, etc.
The pharmaceutical use of crude oil is one reason many people don’t want to
run out!
Natural gas
Methane, mostly
Heat for homes in U.S.
Possible energy source for alternate energy-run automobiles
Burns more completely and cleanly than other fossil fuels
High purity and simple molecules, so low emissions and low pollution
Higher energy output than coal
Gasoline
Fractional distillation does nto provide enough fuel for gasoline
So, we manipulate other fractions and make more gasoline from them
Combination
Cracking
Catalytic Combination
Combine small molecules into a single, larger molecules
Used in making gasoline
4C2H4 C8H18
Cracking
Taking larger molecule fractions and breaking them into smaller ones is cracking
Thermal cracking vs. catalytic cracking
Isomers
Two molecules are constitutional isomers if they have the same molecular formula but different
molecular structures(structural isomers)
Ex. Octane and isooctane
Different shapes
Same formula, same heat of combustion
Isooctane ignites more easily
“Octane Rating”
The octane rating of gasoline denotes its resistance to knocking (preignition)
Pure isooctane= octane rating of 100
Arbitrarily set
Heptanes is less expensive than isooctane, but has an octane rating of zero
87 octane
This gasoline has the same knocking characteristics as a mixture of 87% isooctane and
13% heptanes
Gasoline additives and substitutes
Reformulated gasoline
Oxygenated gasoline
Ethanol
Oxygenated Gasoline
EtOH and MTB E
Octane rating over 100
Made of C, H, and O atoms
Burn more clearly, less CO emissions
Why?—
Reformulated Gasoline
Subset of oxygenated gasoline
Contain lower amounts of very volatile coupounds, like benzene
Highly volatile compounds evaporate easily
Evaporate less easily than “normal” gasoline
Cons:
MTBE is most popular additive but is very soluble in water and is found in water
supplies. Since it is relatively new, risks are still unknown. Animal studies show potential harm
So get fewer emissions but acquire other problems
“must weigh the good with the bad”
MTBE banned, of sorts, in California
Ethanol
From fermenting corn or sugar cane
Or other starch and sugars
C6H12O6 2 C2H5OH +2 CO2
Renewable energy source: crops
Or synthesized:
CH2CH2+ H2O  CH3CH2OH
Energy output: 1376 kJ/mol EtOH, which is less than gasoline
Mix EtOH and gasoline=gasohol
Biodiesal
Other
“P-series”
Garbage
Brief summary of ch.4
This chapter is all about energy: forms sources, and uses
I am looking for a substance that sheds heat quickly and easily. Which one?
The one with the less weight/ lower specific heat
If I want to a substance that holds heat longer, which should I select?
The one with the higher specific heat/ more weight
I want ot know which fuel offers more energy per gram: butane or propane.How can I find out?
1. Calc. BE, DH (per mole)
2. Convert DH to per gram
2C4H10 +13O2 8CO2 + 10H2O
6 (C-C) + 20 (C-H)
| 16 (C-O) + 20(O-H)
+13(O-O)
6 (356) + 2 (416) + 13 (498) | 16 (805) + 20 (467)
16930
|
-22188
DH = -5258 kJ/mol/reaction
5258 kJ/2 mol C4H10 x 1 mol C4H10/58.14 g = 90.434 KJ/g
96.58 kJ/g for propanew