8.1-8.3

Question 1

__% of energy in sunlight reaches earth’s surface and is converted (w/ photosynthesis) to chemical energy (carbohydrates)

Answer 1

0.3%

Question 2

carbohydrates

Answer 2

(CH2O)n
- 2 hydrogen + 1 oxygen / atom of carbon

Question 3

photosynthesis equation

Answer 3

CO2 + H2O –> CH2O + O2

Question 4

products of photosynthesis are..

Answer 4

less stable (by ~ 450 kJ mol-1 carbon) bc of dissociation into atoms

Question 5

green plants __ amount of carbs for their own energy

Answer 5

~1/2

Question 6

reverse reaction of photosynthesis

Answer 6

combustion/respiration
- releases energy

Question 7

respiration

Answer 7

provides aerobic (w/ oxygen) organisms w/ energy needed for functions

Question 8

anaerobic

Answer 8

w/o oxygen

Question 9

what makes up fossil fuels?

Answer 9

• decaying plant matter = buried reduced-carbon compound deposits

dead plant matter + ↑ temps + ↑ pressure = coal, oil, gas
- coal = terrestrial
- oil = marine (lignin)

Question 10

where/how is solar energy stored?

Answer 10

in fossil fuels

Question 11

if we consume all fossil fuels, will we run out of oxygen?

Answer 11

NO…amount of CO2 released = significant bc of small relative amount in atmosphere
- O2 has large relative amount in atmosphere so release of more has low influence

Question 12

total amount of recoverable fossil fuel energy

Answer 12

~ 3.7 x 1019 kJ

Question 13

origin (location) of petroleum and natural gas deposits

Answer 13

marine (oceans)

Question 14

amount of reduced carbon produced through photosynthesis in oceans/year:

Answer 14

25-50 billion tons/year
- mostly recycled atmospheric carbon

Question 15

where is petroleum found?

Answer 15

underground reservoirs (where oceans were historically located or where they currently are)

Question 16

what is petroleum?

Answer 16

crude oil and (refined and unrefined)

Question 17

by what process is methane, ammonia, and water released from sediments in the ocean?

Answer 17

anaerobic bacteria digest buried biological debris

Question 18

organic rearrangement reactions

Answer 18

buried sediment + ↑ temps + ↑ pressure =
↓ bacterial action =
releases CH4 (methane) + light hydrocarbon gases

-gases accumulate in pockets under rock

Question 19

gas hydrates/clathrates

Answer 19

CH4 contained undersea/permafrost
- hydrogen-bonded H2O molecules surround CH4 –> form solid material
- stable @ ↓ temp/↑ pressure)
- found @ 300+ m. depth

Question 20

what is the largest component of natural gas?

Answer 20

methane

Question 21

what produces the largest amount of stored methane?

Answer 21

• anaerobic bacteria = trapped @ depth/cold temp in water
• methane deposits = amnt > (coal + oil + gas)
• no practical method for extraction (w/o releasing large amnts of CH4 into atmosphere)

Question 22

abiotic hydrocarbons produce methane when…

Answer 22

hydrocarbons + ↑ depth + ↑ temp + ↑ pressure = carbonate rock –> (reduced) –> CH4

Question 23

13/12C isotope

Answer 23

• ↓ in organic compounds (derived from living matter) bc heavier isotope
• reacts slowly (in photosynthesis)

Question 24

CH4 samples = __ in 13/12C @ increasing depths; what does this mean?

Answer 24

increases
- there is likely an abiotic source (but it’s unknown)

Question 25

world petroleum depletion/over

Answer 25

heavy depletion/over

Question 26

origin (location) of coal

Answer 26

terrestrial
- remains of woody plant matter ~250 million y.o.

Question 27

components of woody plants

Answer 27

mostly lignin + cellulose

Question 28

when a plant dies, aerobic bacteria…

Answer 28

rapidly oxidize cellulose (carb) –> CO2 + H2O

Question 29

why don’t aerobic bacteria oxidize lignin?

Answer 29

lignin is resistant to bacterias

Question 30

structure of lignin

Answer 30

complex, 3-D polymer based on benzene rings

Question 31

coniferous plants

Answer 31

cone-bearing seed plants; never lose leaves
- pines/cedars

Question 32

deciduous plants

Answer 32

perennial plant; seasonally loses leaves/stems
- oaks/shrubs

Question 33

building units of lignin in coniferous plants

Answer 33

coniferyl alcohol

Question 34

building units of lignin in deciduous plants

Answer 34

sinapyl alcohol

Question 35

peat

Answer 35

in swamps: lignin accumulates under water and compacts into layers

Question 36

components of coal

Answer 36

peat layers + time + ↑ temp + ↑ pressure

Question 37

process of lignin –> coal

Answer 37

• lignin lose O (expulsion of H2O + O2 gas)
• bonds form
• produces hard, black, carbon-rich coal

Question 38

what will peat produce if given excess time?

Answer 38

graphite
- pure carbon; C in layers of benzene rings

Question 39

.

Answer 39

.

Question 40

how is chemical energy released from fuels?

Answer 40

explosion/combustion!
- w/ heat: energy from forming bonds > energy breaking bonds

Question 41

enthalpy

Answer 41

energy required dissociate molecules

Question 42

calculating enthalpy

Answer 42

enthalpy = (total combustion enthalpy + total bond enthalpy) / (# of molecules)
- varies based on molecule

Question 43

trends in bond dissociation enthalpies:

Answer 43

• closer valence electrons = ↑ bond
• ↑ nuclear energy = ↑ electronegativity
• attraction of unlike charges ↑ bond energy
• ionic bonds > non-ionic bonds
  o double bonds > single bonds

Question 44

which is stronger: bonds between 2 of the same molecules or bonds between 2 different molecules?

Answer 44

2 same atoms bond < 2 diff atoms bond