3.1.1 Carbon based fuels Flashcards
1
Q
fuel
A
stores chemical potential energy that can be released relatively easily
2
Q
chemical energy/heat content/enthalpy
A
energy contained by chemical compound stored in its bonds (sum of potential and kinetic energy of substance including rotations, vibrations and movement of electrons, repulsion and attractions within and between electrons and nuclei
3
Q
enthalpy change
A
exchange of heat energy between system and surroundings under constant pressure
Hp-Hr
4
Q
combustion
A
substance reacting with oxygen gas releasing energy
5
Q
exothermic
A
- enthalpy change negative
- release energy so surroundings get hotter
- bonds of products are stronger and more stable
6
Q
endothermic
A
- enthalpy change positive
- absorb energy so surroundings get colder
- bonds of reactants are weaker and less stable
7
Q
activation energy
A
energy required to break bonds of reactants so reaction can proceed
8
Q
fossil fuel
A
- formed from ancient plants, animals, microorganisms buried under tonnes of mud, sand and rock undergoing complex change to become fossil fuel
- organic matter still retains some chemical energy accumulated by photosynthesis
9
Q
non renewable
A
- used faster than can be replaced since they take millions of years to form
10
Q
coal
A
- large molecules like C, H, N and S
- wood and plant materials
11
Q
coal heat content changes
A
- as carbon content increases, proportion of H and O decrease so heat released increases
12
Q
petrol (crude oil)
A
- mixture of liquid hydrocarbon molecules (mostly alkanes)
- useful compounds like petrol and petrodiesel separated by fractional distillation
13
Q
crude oil use
A
hot gas formed by combustion moves pistons up and down
14
Q
natural gas
A
methane with small amounts of hydrocarbons (undergoes more pressure than crude oil)
15
Q
natural gas found in…
A
- found in gas reservoirs between rock layers, petroleum deposits, coal deposits
- coal seam gas: pressure of water on coal seams keeps gas adsorbed to coal surface
- accessed by drilling to allow gas to flow to surface
16
Q
natural gas use
A
- fuel combustion causes air to expand spinning turbine and generator
17
Q
biofuel
A
fuels derived from plant material like grains, sugar cane, vegetable waste and vegetable oil
18
Q
renewable
A
energy that can be obtained from natural resources that can be constantly replenished in a short period of time
19
Q
biofuels CO2
A
- plant materials photosynthesise meaning that CO2 is removed from atmosphere
- however CO2 is still released when burnt
- CO2 is also released in farming, fertilisation and transport
20
Q
biogas
A
- released in the breakdown of organic waste by anarobic bacteria that decompose complex molecules like carbs and proteins into CO2 and CH4 in a digester
21
Q
biogas feedstock->usage
A
- rotting rubbish, decomposing material used in small scale electricity generators onsite of biogas production (e.g. farms, sewage works, piggeries, rubbish tips)
22
Q
biogas advantages
A
- renewable
- made from waste thus reducing waste
- further waste can be made into fertiliser
- low running cost
- CO2 absorbed in photosynthesis
23
Q
biogas disadvantages
A
- low energy content because methane gas not pure
- supply of waste raw materials limited
24
Q
biodiesel
A
- mixture of organic compounds called esters
- produced from vegetable oils, animal fats and alcohol
25
biodiesel process (transesterification)
- warming with alcohol with KOH as catalyst
- forming 3 ester molecules (biodiesel C19H38O2) and glycerol
26
triglyceride
molecular structure consisting of 3 hydrocarbon chains attached by ester functional group to backbone of C atoms
27
saturation biodiesels
- saturated (single bond) from animals
- unsaturated (double bond) from plants
28
biodiesel advantages
- 20% can be blended with petroleum diesel as transport fuel
- doesn't require engine modification
- lubricant properties reduces wear and tear on engines
- biodegradable
- low emission of pollutants
29
coal advantages
- large reserves
- easier transport
- relatively high energy content
- cheap/easily mined
30
biodiesel disadvantages
- economically unfavourable
- emits more nitrogen oxides
- high viscosity(thick/doesn't flow) means unsuitable in cold climates
- destruction of natural habitats and land that could be used for food
31
coal disadvantages
- non renewable
- high level of emissions
- mining causes environmental damage
32
petrol advantages
- high energy content
- ease of transport
- transport and chemical industry uses
33
petrol disadvantages
- non renwable
- polluting although less than coal
- limited reserves
- oil rigs can cause environmental damage
34
natural gas advantages
- more efficient than coal
- easily transported through pipes
- relatively high energy content
- less CO2/particulate matter
- adjustable to fluctuating power demands
35
natural gas disadvantages
- non renewable
- limiting reserves
- polluting but less than coal and petrol
- export as LNG increases energy density but increases energy used
36
bioethanol fermentation
- natural process where organism converts carbohydrate into alcohol
1. carbohydrates pulped with water to break up plant/cell structure
2. enzymes in yeast break up carbohydrates molecules to from glucose
3. glucose fermented at 35 degrees to produce ethanol solution
37
fermantation pretreatment
- stronger hydrogen bonding in cellulose means more treatment (saccarification) needed break molecules up
- sugar cane has smaller more soluble sucrose molecules which don't need pretreatment
38
fermentation distillation
- process of separating components or substances from liquid mixture using selective boiling points and condensation
1. solution heated to boiling then fed into tall distillation columns
2. temp controlled so water (bp 100) falls to bottom and ethanol gas (bp 79) rises to top
3. further microfiltration and dehydrating agents
4. small amounts methanol added to make unfit for human consumption
39
E10 advantages
- cheaper
- cleaner combustion
- can be renewable
- lower net CO2 emissions dues to absorption during formation
- safer production
40
E10 disadvantages
- lower energy content due to carbon atoms already being partly oxidised by presence of oxygen atoms
- high % ethanol can damage car engines
- crops needed for food sources as well
41
photosynthesis
- endothermic reaction in chloroplasts of cells of green plants only
- converts light into chemical energy
42
cellular respiration
- primary source of energy of cells of plants and animals
- exothermic
43
carbohydrates
- CHO
- during digestion enzymes in saliva and small intestine break starch molecules back to glucose which is transported to body cells by blood
- energy is required to form many bonds in large carbs so energy released is large
44
fats and oils
- triglycerides are broken down and oxidised into CO2 and H2O
45
proteins
- amino acids joined by peptide link
- rarely used as energy since have other important roles
- important to quickly replace proteins to ensure functioning of other processes
46
enzyme
organic catalyst that alter rate of biochemical reactions
47
metabolism
digesting nutrients into smaller molecules
48
nutrients
substances used by organisms to survive grow and reproduce
49
energy content
heat of combustion
50
energy value
energy available to body from nutrients or food (less because some energy lost as heat in combustion)
51
comparing energy values
- carbs contain more oxygen atoms than fats and oils so carbon atoms are already partly oxidised (higher degree of oxidation) thus fats and oils have greater potential for oxidation and release more energy
52
fibre
can't digest, imcomplete absorption during digestion
53
heat of combustion
energy released when specific amount of substance burns completely in oxygen (+)
enthalpy would be (-)
