carbon-based fuels AOS1

Question 1

what reactions are fuels involved in?

Answer 1

combustion reactions where a substance reacts with oxygen gas, releasing energy in the form of heat

Question 2

endothermic vs exothermic reactions?

Answer 2

endothermic=reactions that absorb energy, exothermic=
reactions that release energy

Question 3

what’s enthalpy change?

Answer 3

a measure of the quantity of energy absorbed or released during chemical reactions, it’s determined by subtracting the enthalpy of the reactant from the enthalpy of the products

Question 4

enthalpy change in exothermic reactions?

Answer 4

total energy of the reactant is higher than total energy of the products, energy released when the bonds in the products form is greater than the energy required to break the bonds in the reactants, delta H is negative and excess energy is released to the surroundings

Question 5

enthalpy change in endothermic reactions?

Answer 5

total chemical energy of the reactant is lower than that of the products, energy released when the bonds in the products form is less than the energy required to break the bonds in the reactants, the energy required is absorbed from the surroundings and the delta H is positive

Question 6

what’s the activation energy?

Answer 6

the energy required to break the bonds of reactants so that a reaction can proceed, it exits for both endothermic and exothermic reactions

Question 7

what’s a thermochemical equation?

Answer 7

a balanced chemical equation that includes the enthalpy change (delta H)

Question 8

what do energy profiles show?

Answer 8

they represent the energy changes in a reaction, the activation energy is often higher in endothermic reactions whilst their delta H is smaller

Question 9

main uses of energy in AUS?

Answer 9

for transportation + heating

Question 10

what are the future energy needs of the world?

Answer 10

using renewable fuels that can be replaced at a sustainable rate for large-scale energy product so these should be reliable, sustainable and cost-effective, fuels are considered renewable if they can be replaced at a sustainable rate

Question 11

what are non-renewable resources?

Answer 11

those that are used faster than they’re replaced, examples are coal/oil/natural gas and reserves of fossil fuels are limited so they could eventually be exhausted

Question 12

what are fossil fuels?

Answer 12

naturally occurring fuels like coal that were formed in the geological past from the remains of living organisms, the chemical energy in fossil fuels can be considered to be trapped solar energy, occurred million years ago so its been as non-renewable

Question 13

what’s coal?

Answer 13

as wood and other plant material is converted into coal, the carbon content increases and the proportion of hydrogen + oxygen decreases, coal is a mixture of large molecules made from carbon, hydrogen, sulfur, nitrogen and other elements, its chemical energy is converted to electrical energy at a power station (combustion of coal approx 32kJg-1)

Question 14

what are the energy transformations involved in burning coal to produce electricity?

Answer 14

chemical energy in coal -> thermal energy of burning coal -> thermal energy of steam -> mechanical energy of turbine -> electrical energy from generator

Question 15

what’s petrol?

Answer 15

also known as crude oil is a mixture of hydrocarbon molecules (like octane) that are mostly members of the homologous series of alkanes, extracted through fractional distillation, it ranges in length from 5 to 12 carbon atoms, petrol is often contaminated with sulfur producing sulfur dioxide when burned

Question 16

what’s fractional distillation?

Answer 16

doesn’t produce pure substances instead separates compounds into fractions which can be used as fuels or treated further to produce more specific products through chemical processes, petrol is one of the fractions obtained from crude oil, diesel (petrodiesel) is another fraction of crude oil but the alkanes in petrodiesel is slightly longer than those in petrol

Question 17

what’s natural gas?

Answer 17

a fossil fuel found in deposits in the Earth’s crust. it’s mainly composed of methane together with small amounts of other hydrocarbons like ethane/ propane and h20,sulfur, CO2 and nitrogen may also be present in it

Question 18

where is natural gas found?

Answer 18

in gas reservoirs trapped between layers of rocks, as a component of petroleum deposits and it coal deposits where it’s often bonded to the surface of coal, the pressure of the water it contains can keep the gas absorbed to the coal surface

Question 19

how it natural gas extracted?

Answer 19

can be found attached to/trapped above coal -> CSG (coal steam gas) and by drilling, like with crude oil, which allows the natural gas to flow to the surface, also can be used in liquid form (LNG) but this conversion increases energy density and the liquification consumes a great quantity of energy

Question 20

what’s a gas-fired power plant?

Answer 20

used to generate electricity for the power grid from natural gas and methane + other small alkanes are burnt to release energy, the process is simpler than that for coal as the thermal energy from steam simply is used to generate electrical energy

Question 21

what are biofuels?

Answer 21

fuels derived from plants or animals that can usually be replenished at a sustainable rate hence they’re considered forms of renewable energy, they have a lower environmental impact

Question 22

what’s renewable energy?

Answer 22

energy that can be obtained from natural resources that also can be constantly replenished

Question 23

what are the main types of biofuels?

Answer 23

bioethanol, biogas and biodiesel which can be used alone or blended with fossil fuels like diesel

Question 24

are biofuels carbon neutral?

Answer 24

in theory, a biofuel could be carbon neutral, absorbs the same amount of CO2 in its formation as is released in its combustion however in practice energy is required to farm, fertilises + transport biofuels so they’re not likely to be fully carbon neutral

Question 25

what’s biogas?

Answer 25

a gas that’s released in the breakdown of organic waste by anaerobic bacteria which decompose the complex molecules contained in susbstances like protein into the simpler molecular compound like CO2 + CH4, this is done using a digester which is a large tank filled with anaerobic bacteria that digest the complex molecules to form biogas

Question 26

what’s biogas mainly made up of?

Answer 26

methane (approx 60%, then CO2) and can use things like rotting rubbish and decomposing plant material to be produced

Question 27

can electricity be produced from biogas?

Answer 27

it’s usually used in small-scale electricity generators which are often located at the site where the biogas is produced, the main reaction that occurs in the combustion of biogas is the same reaction as that of a gas-fired power station, combustion of methane but the energy energy is a lot lower than that of natural gas because biogas possesses a significantly lower methane content

Question 28

what’s biodiesel?

Answer 28

a mixture of organic compounds called esters which are produced by a chemical reaction between veggie oils/animal fats and an alcohol. the usual raw material for the production of biodiesel is veggie oil from sources like palm oil. fats + oils are triglycerides with a molecular structure consisting of 3 hydrocarbon chains each attached by an ester functional group to a backbone of 3 carbon atoms

Question 29

what do triglycerides do for biodiesel?

Answer 29

the triglyceride is converted not biodiesel by warming it with an alcohol usually methanol/ ethanol in the process of transesterification and concentrated KOH is often the catalyst in this reactions

Question 30

what occurs in the transesterification reaction of biodiesel?

Answer 30

the triglyceride is converted into a small molecule (glycerol) and 3 ester molecules with long carbon chains, the ester molecules are the biodiesel product and this biodiesel can be used as the fuel for some diesel engines

Question 31

summary of what biodiesel is?

Answer 31

esters of fatty acids that are formed from the reaction between triglycerides and small alcohol molecules, produced from triglycerides in animal fats or plant oils which react with methanol in a transesterification reaction to form biodiesel

Question 32

biggest players in the electricity industry for sustainability?

Answer 32

currently its wind, solar and hydro in that order

Question 33

what’s a common disadvantage of biofuels?

Answer 33

a lower energy content and the limited supply of raw (sometimes waste) material needed + the requirement of fertile + arable land

Question 34

what are the advantages of coal?

Answer 34

large reserves, less easily transported than liquid or gaseous fuels and relatively high energy content

Question 35

what are the advantages of natural gas?

Answer 35

more efficient than coal for electricity production, easy to transport through pipes and relatively high energy content

Question 36

what are the advantages of petrol?

Answer 36

high energy content + ease of transport

Question 37

what’s the change in enthalpy for photosynthesis?

Answer 37

+2803kJ

Question 38

what plays a large role in the amount of energy obtained by our bodies from food?

Answer 38

the type of bonding in the nutrient

Question 39

what are carbohydrates?

Answer 39

are made from elements like carbon, hydrogen + oxygen, often they’re polymers of glucose like starch

Question 40

what are fats and oils

Answer 40

examples of triglycerides, large non-polar molecules with 3 long hydrocarbon chains attached to a glycerol molecule, they provide and store energy in the body

Question 41

what are proteins?

Answer 41

they’re rarely used in the body as an energy source, hydrogen bonds are often in them

Question 42

fibres for energy?

Answer 42

humans cannot digest most fibre so the energy it contains isn’t available to humans

Question 43

how is bioethanol produced?

Answer 43

produced from glucose and other sugars (carbs/sugars) in a fermentation process -> biomass, various enzymes + microorganisms catalyse or facilitate the reactions involved and is carried out at 35C degrees because if it was higher the enzymes/ microorganisms would be destroyed

Question 44

what’s fermentation?

Answer 44

a natural process where an organism converts a carb like starch/sugar into an alcohol

Question 45

main (future) bioethanol feedstocks?

Answer 45

sugar cane which is high in sucrose, wheat which is high in starch and forest waste which is high in cellulose

Question 46

what’s the process of bioethanol fermentation?

Answer 46

carbs are piped with water (process involving blending the biomass in h20 to break up the cell/plant structures), various enzymes are then added to the mixture to break the carb molecules down to form glucose and then exams catalyse the fermentation of glucose to produce an ethanol solution

Question 47

what’s distillation?

Answer 47

process of separating components/substances from a liquid mixture by using selective boiling and condensation as ethanol has a lower boiling point than water

Question 48

why is distillation used for bioethanol/ethanol?

Answer 48

to further operate the ethanol from the water so it can be used as a fuel and this process uses different boiling points to seperate the liquids, after this micro-filtration and dehydrating agents are used to further remove traces of water in the ethanol, a significant amount if energy is needed to boil the ethanol solution so the great energy requirements means that the production of bioethanol isn’t carbon-neutral + a larger mass of ethanol is required to provide the same quantity of energy which petrol creates

Question 49

what’s the difference between E10 and petrol?

Answer 49

E10 (bioethanol is sold as E10 which is a mixture of petrol and ethanol) has a lower energy density than petrol but has a cleaner combustion process + can be a renewable fuel and is partially carbon-neutral (lower CO2 emissions, less bad effect), but for petrol there’s also less CO2 produced per km when driving

Question 50

what are the requirements of combustion reactions?

Answer 50

fuels to burn, oxygen for the fuel to burn in and energy to initiate the process

Question 51

what is oxygen in a combustion reaction?

Answer 51

often a reactant

Question 52

what are the products of incomplete combustion?

Answer 52

carbon monoxide and/or carbon solid and water so when it burns there’s a yellow/smoky/sooty flame due to the presence of glowing carbon particles

Question 53

what conditions are the heat of combustion measure at?

Answer 53

usually 298K and 100kPa which means that water is a liquid and only fuels that exist as pure substances can have their heat of combustion measured in kJ mol-1

Question 54

what’s enthalpy?

Answer 54

chemical energy of a substance and the change in enthalpy is the difference in chemical energy of products compared to the reactants

Question 55

what does heat of combustion indicate?

Answer 55

the maximum quantity of energy that can be released when a specified amount of fuel undergoes complete combustion

Question 56

what’s fracking?

Answer 56

formed from the remains of plants and animal materials. It is found in deposits in the Earth’s crust and can be accessed by drilling. It is then extracted from coal and shale deposits by fracking. Fracking involves injecting liquid at high pressure into coal and shale rocks to force open fissures (cracks) to extract the gas. Materials used for this process have have harmful impacts on the surrounding environment as well water supplies

Question 57

what’s fractional distillation?

Answer 57

Fractional distillation utilises the different boiling points of the many different compounds present in petroleum to separate them. The separated fractions can then be used as fuel or can be treated to produce desired products. Used for petrol/crude oil