Chemistry
Glucose (a simple sugar) is created in the plant by photosynthesis.
- 6 CO2 + 6 H2O + light → C6H12O6 + 6 O2
During ethanol fermentation, glucose is decomposed into ethanol and carbon dioxide.
- C6H12O6 → 2 C2H5OH+ 2 CO2 + heat
During combustion ethanol reacts with oxygen to produce carbon dioxide, water, and heat:
- C2H5OH + 3 O2 → 2 CO2 + 3 H2O + heat
After doubling the combustion reaction because two molecules of ethanol are produced for each glucose molecule, and adding all three reactions together, there are equal numbers of each type of atom on each side of the equation, and the net reaction for the overall production and consumption of ethanol is just:
- light → heat
The heat of the combustion of ethanol is used to drive the piston in the engine by expanding heated gases. It can be said that sunlight is used to run the engine (as is the case with any combustion-based energy source, as sunlight is the only way energy is added to the planet, and geothermal energy, which comes from the heat already present inside the earth).
Glucose itself is not the only substance in the plant that is fermented. The simple sugar fructose also undergoes fermentation. Three other compounds in the plant can be fermented after breaking them up by hydrolysis into the glucose or fructose molecules that compose them. Starch and cellulose are molecules that are strings of glucose molecules, and sucrose (ordinary table sugar) is a molecule of glucose bonded to a molecule of fructose. The energy to create fructose in the plant ultimately comes from the metabolism of glucose created by photosynthesis, and so sunlight also provides the energy generated by the fermentation of these other molecules.
Ethanol may also be produced industrially from ethene (ethylene). Addition of water to the double bond converts ethene to ethanol:
- C2H4 + H2O → CH3CH2OH
This is done in the presence of an acid which catalyzes the reaction, but is not consumed. The ethene is produced from petroleum by steam cracking.
When ethanol is burned in the atmosphere rather than in pure oxygen, other chemical reactions occur with different components of the atmosphere such as nitrogen (N2). This leads to the production of nitrous oxides, a major air pollutant.
Read more about this topic: Ethanol Fuel
Famous quotes containing the word chemistry:
“If thought makes free, so does the moral sentiment. The mixtures of spiritual chemistry refuse to be analyzed.”
—Ralph Waldo Emerson (1803–1882)
“Science with its retorts would have put me to sleep; it was the opportunity to be ignorant that I improved. It suggested to me that there was something to be seen if one had eyes. It made a believer of me more than before. I believed that the woods were not tenantless, but choke-full of honest spirits as good as myself any day,—not an empty chamber, in which chemistry was left to work alone, but an inhabited house,—and for a few moments I enjoyed fellowship with them.”
—Henry David Thoreau (1817–1862)
“The chemistry of dissatisfaction is as the chemistry of some marvelously potent tar. In it are the building stones of explosives, stimulants, poisons, opiates, perfumes and stenches.”
—Eric Hoffer (1902–1983)