Fuel Science 431

3 ways to use fuel
1. release energy thru combustion
2. chemical conversion to another fuel form
3. conversion to non-fuel material
a fuel’s use and behavior is determined by…
…its chemical comnposition and molecular structure
define fuel science
the study of the origin, composition and properties, and fundamental chemical rxns of fuels
carbon content of common fuels
natural gas: 75% C
petroleum: ~85% C
coal: 65-95% C
biological markers
indicate an origin from living matter
two important porphyrins
chlorophyll
heme
global carbon cycle
atmospheric CO2 is taken into plants, passes thru animals, and accumulates in dead organisms, which decay and release it back into the atmosphere
free energy change of photosynthesis?
delta G= +2720 kJ
VERY endothermic
equilibrium constant of 1E-47!
What about the organic matter that doesn’t completely decay?
organic matter which escapes complete decay is preserved and accumulated, which we can burn as fuel (releasing that energy)
reverse of photosynthesis rxn
decay rxn
Why do we have large accumulations of carbon-based fuels?
Because most organic rxns do not go to completion
to maximize accumulation of carbon-based fuels…
1. abundant light for photosynthesis 2. warmth for fast rxns 3. minimum exposure of organic matter to oxygen
oxygen can participate in decay by…
1. direct rxn of atmospheric O2
2. direct rxn of O2 dissolved in water
3. indirectly via aerobic bacteria
ideal environments for life and then prevention of decay of organic matter
1. freshwater lakes where a bottom layer of relatively cold anearobic water lies under a layer of warmer, aerobic water
2. marine environments where up-welling of water spreads an anearobic layer over the continental shelf
protein functions
transport of nutrients
structural components of cells
enzymes
peptide
two or more amino acids linked to each other
key features of protein composition and structure
peptide bonds are reversible
contain significant amounts of oxygen and nitrogen
simple sugar naming
1. number of C in the chain: pentose, hexose
2. presence of aldehyde or ketone group: aldose, ketose
3. both: aldohexose, ketopentose
aldehyde + alcohol
-> hemiacetal
ketone + alcohol
-> hemiketal
many simple saccharides are cyclic because…
…they contain both an alcohol and aldehyde/ketone group, so the molecule reacts with itself and forms a ring
hemiacetal/hemiketal + alcohol
-> acetal/ketal
anomeric carbon
the carbon at which the hemiacetal/hemiketal forms
for each hemiacetal/hemiketal, two anomers exist:
1. alpha: OH and CH2OH are trans
2. beta: OH and CH2OH are cis
glycoside linkage
the acetal linkage between monosaccharide units in a polysaccharide
glucoside linkage
a glycoside linkage, where the monosaccharides are glucoses
cellulose
made of glucoses linked by beta (trans) glucoside linkage
starch
made of glucoses linked by alpha (cis) glucoside linkage
amylose
linear starch
amylopectin
branched starch
key features of carbohydrate composition and structure
contain cyclic structures
high oxygen content (weight basis)
lipids
naturally occuring compounds which yield fatty acids upon hydrolysis
waxes
esters of long chain alcohols with fatty acids
fats and oils
esters of long chain carboxylic acids joined by glycerol
key features of lipid composition and structure
formation is reversible
relatively rich in hydrogen
relatively poor in oxygen
lignin
a constituent of cell walls that provides extra rigidity for woody plants
a “bio-polymer” made of three alcohols
has abundant cyclic aromatic structures and a high proportion of oxygen
two main types of organic matter
1. low-oxygen chain structures (hydrocarbons, lipids), mostly from organisms living in water
2. high-oxygen cyclic structures (carbohydrates, lignin), mostly from higher plants
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