Fuels

Question 1

what are the fossil fuels

Answer 1

coal, oil and natural gas

Question 2

what are non-renewable resources

Answer 2

those that are used faster than they can be replaced

Question 3

why are fossil fuels non-renewable

Answer 3

reserves of fossil fuels are limited and could eventually be exhausted

Question 4

what are fossil fuels

Answer 4

non-renewable fuels that are derived from plant or animal matter

Question 5

process of coal formation

Answer 5

1. plants that die in ancient wetlands are only partially decomposed due to anaerobic and acidic conditions, forming peat
2. Peat is buried under layers of sediment due to rising sea levels. the buried peat is subjected to heat and pressure
3. After millions of years of heat and pressure, coal is formed
   4.Coal is mined from the ground to be combusted in power plants for electricity

Question 6

what is coal composed of

Answer 6

primarily carbon (and water)

Question 7

“crude”

Answer 7

not refined

Question 8

distillation

Answer 8

boiling to evaporate and then condensing into a liquid

Question 9

coal burning reaction

Answer 9

C(s) + O2(g) = CO2 (g) (+ 32KJg-1)

Question 10

what happens as we go down the layers of coal

Answer 10

the water content decreases and carbon content increases which results in the increase of energy content of the coal

Question 11

why does less water in coal result in a higher energy conetnt

Answer 11

less water is needed to be vaporised, therefore the amount of heat released is greater

Question 12

why does energy content increase with coal content in carbon

Answer 12

the more heat is released when is it burned

Question 13

what is the overall efficiency of a coal-fired power station and why

Answer 13

30-40%, energy is lost in each step of the process (the more energy transformations, the less efficient the process)

Question 14

steps in the formation of oil and natural gas

Answer 14

1. ancient sea animals and plants die and their bodies fall to the sea floor, where anaerobic conditions prevent complete decomposition 2. plant and animal remains are covered by layers of sediment and subjected to heat and pressure over millions of years 3. after millions of years, oil and gas deposits are formed

Question 15

natural gas

Answer 15

composed of mainly methane together with small amounts of ethane and propane, (water, sulfur, carbon dioxide and nitrogen may be present)

Question 16

equation of the combustion of methane (natural gas)

Answer 16

CH4(g) + 2O2(g) = CO2(g) + 2H2O (l)

Question 17

where is natural gas found

Answer 17

natural gas deposits are often found trapped above crude oil, once a well is sunk into the deposit, the natural gas flows to the surface

Question 18

crude oil

Answer 18

a thick, sticky black liquid which is composed of a complex mixture of lots of different hydrocarbon compounds of different sizes

Question 18

where is crude oil found

Answer 18

in pourous rock (under the ground and under the sea)

Question 19

why is crude oil a finite resource?

Answer 19

it is being used up much faster than it is being formed

Question 20

how is crude oil converted into a useable form

Answer 20

it must be fractionally distilled and then cracked to obtain useful fuels such as petrol

Question 21

how are componenets of crude oil sepearted during fractional distillation

Answer 21

each fraction consists of groups of hydrocarbons of similar chain lengths, these molecules therefore have similar properties and boiling points

Question 22

petrodiesel

Answer 22

a fraction of crude oil that cintains slightly longer molecules than those in petrol

Question 23

why is petrodiesel an undesirable fuel

Answer 23

when petrodiesel is contaminated with sulfur and nitrogen, it is burned and it produces sulfuric acid and nitric oxide, which have many negative effects on the environment

Question 24

biofuels

Answer 24

renewable resources that are derived from plants which can be easily grown and harvested

Question 25

why are biofuels carbon neutral

Answer 25

plants initially remove CO2 from the atmosphere which is then releasesd when burning the biofuels, hence there is no net increase in the amount of CO2 in the atmosphere

Question 26

why are biofuels relastically not carbon neutral

Answer 26

energy is required to farm, fertilise and transport biofuels

Question 27

biogas

Answer 27

when organic materials decays in anaerobic conditions and a micture of gas is produced, composed of mainly methane and carbon dioxide

Question 28

how is biogas produced (steps)

Answer 28

1. organic matter used as a fertiliser (containing carbohydrates) for crops
2. anaerobic bacteria decompose the organic waste
3. CH4 is burnt for heating, cooking or electricity

Question 29

euqation for the formation of biogas

Answer 29

C6H12O6 (s) = 3CO2 (g) + 3CH4 (g)

Question 30

bioethanol

Answer 30

dervied from plant materials which contains many carbohydrates, the plant material is combined with water and anaerobic bacteria whcih ferment glucose to produce ethanol and CO2

Question 31

how is bioethanol produced

Answer 31

via fermentation

Question 32

fermentation process

Answer 32

sugar or starch is dissolved in water and yeast is added, the mixture is then fermented between 15–35 degrees celcius in the absence of oxygen for few days. various enzymes/microorganisms catalyse or facilicate the reactions involved

Question 33

equation for fermentation

Answer 33

C6H12O6(aq) = 2C2H5OH(aq) + 3CO2(g)

Question 34

how is glucose produced from carbohydrates

Answer 34

the carbohydrates are pulped with water, a process that involves blending the biomass in water to break up the cell or plant structures. various enzymes are then added to the mixture to break the carbohydrate down into glucose

Question 35

what is the formation of carbohrates into glucose called

Answer 35

pre-treatment

Question 36

how does the level of pre-treatment change

Answer 36

the stronger the bonding in the carbohydrate feedstock the greater the pre-treatment required to ensure the enzymes are effective

Question 37

why is forest waste difficult to produce bioethanol

Answer 37

cellulose is abundent in forest waste but difficult to process as the hydrogen bonds holding the cellulose molecules together are relatively strong

Question 38

distillation

Answer 38

occurs after fermentation, uses different boiling points of liquids to seperate them (water has a higher boiling point than ethanol)

Question 39

why is distillation required

Answer 39

are fermentation a dilute ethanol solution is produced which must be seperated from the reaction mixture to be useful as a fuel

Question 40

bioethanol is comparison to petrol

Answer 40

can damage engines, has 62% energy content of petrol

Question 43

biodiesel

Answer 43

made from vegtable oils and animal fats which are composed of triglycerides, used primarily as a transport fuel

Question 44

triglycerides

Answer 44

three fatty acid residues, each bonded to a glycerol molecule via an ester group

Question 45

how are triglycerides converted to biodeisel

Answer 45

via transesterification

Question 46

transesterification

Answer 46

a reaction between a triglyceride and methanol to produce biodeisel and glycerol in the presence of a ctalyst (KOH)

Question 47

what does the structure of a triglyceride depend on

Answer 47

the plant/ animal used as a source (saturated = animals, unsaturated = plants)

Question 48

saturated esters

Answer 48

conatin only single C-C bonds, the fatty acid chain is straight, which allows the molecules to pack closely together to form a solid and room temp

Question 49

unsaturATED ESTERS

Answer 49

contain the presence of a double carbon bond, this causes a kink in the fatty acid chain, preventing the molecules from packing in closely together, hence they are liquids at room temp (as dispersion forces are weakened between neighbouring molecules)