carbon based fuels - Unit 3 AOS 1 Flashcards
Fuel
- fuels are substances used to produce energy
- they have chemical energy stored in them which can be converted into electrical energy
- it is usually reacted with oxygen to produce energy
uses of fuels
- ## local level (petrol in car)
renewable fuel
- one that can be replenished by natural processes within a relatively short period of time.
- they are sustainable and the chances of these fuels running out is very low.
non-renewable fuel
- one that cannot be replenished at the rate it is used
Fossil fuels
- fuels formed under the earth’s crust from the chemical decomposition of plant and animal matter
- contains chemical energy that can be converted into electrical, heat or chemical energy
- chemical decomposition takes a long period of time
- created by fossilisation where a dead organism is buried in relatively low oxygen conditions under intense pressures and heat
coal
- a black or brown rock consisting of carbonised plant matter formed from the effects of pressure, heat and moisture.
- a mixture of large molecules made from hydrogen, nitrogen and sulphur formed by the partial decay of plant and animal matter
- vegetation - peat - brown coal - black coal
- from peat to black coal, water content decreases and carbon and energy content increases
- coal is bad for the environment as the combustion of it produces carbon dioxide
petrol (crude oil)
- a mixture of hydrocarbons under the earths crust
- the hydrocarbons have different chain lengths
- is not useful itself as a fuel but contains many useful compounds
- separated by fractional distillation
fractional distillation of crude oil
- crude oil has a mixture of different hydrocarbons, each with different chain lengths
- the longer the molecule, the stronger the intermolecular forces will be, requiring more energy to be broken
- long molecules - higher boiling points
- short molecules - lower boiling points
fractional distillation of crude oil process
- crude oi is heated to a high temperature outside of the fractionating column
- when it is a t a certain temperature, it will be pumped into the bottom of the column
- at the bottom of the chamber where the temperature is high, some long chain molecules return to liquid and are collected at the bottom
- molecules rise up the column making their way through vents
- depending of molecules boiling points, they will eventually get too cool and condense to liquid where they can be collected in their tray.
- molecules with low boiling points will condense much high in the column
natural gas (coal seam gas)
- found under the earths crust in coal deposits, in layers of rocks or in petroleum deposits
- composed of methane and other hydrocarbons
- it accessed by drilling and extracted by fracking
renewability of fossil fuels
energy efficiency of fossil fuels
environmental impact of fossil fuels
- fossil fuels are considered non-renewable because they take a long time to form and so cannot be replenished quickly or at the rate they are used
- fossil fuels are more energy efficient.
- burning fossil fuels can produce pollutants such as SO2, contributing to acid rain
- accumulation of gases in the atmosphere can add to the greenhouse effect
- drilling disrupts natural landscapes
bio fuels
- sourced from organic matter such as wheat, sugarcane and soy
biogas
- a mixture of gases released by the anaerobic breakdown of organic matter
- mostly composed of methane and carbon dioxide
- bacteria breakdown complex molecules into smaller compounds
- variuos macromolecules broken down tp produce the gas (carbohydrates and proteins)
biodiesel
- a mixture of organic compounds called esters that are produced from combining fats and alcohol in a transesterification reaction.
- triglyceride + methanol → fatty acid methyl esters + glycerol
bioethanol
- a fuel produced by the fermentation of sugars and starches into organic matter called biomass
- conducted by yeast
- glucose solution → bioethanol solution + carbon dioxide
- fermentation conducted by yeast followed by distillation to remove water
- the ethanol needs to be separated from water
- it goes from 5-21% V/V to 100% V/V
renewability of biofuels
energy efficiency of biofuels
environmental impact of biofuels
- biofuels are considered renewable because they can be replenished quickly
- biofuels are less efficient that due to the presence ox oxygen. They require more fuel to produce the same amount of energy.
- bioethanol is carbon neutral because the production of it released carbon dioxide however this is taken in by plants through photosynthesis. - This means there is no net production of carbon dioxide.
- biofuels are good foe waste management
- they are already partially oxidised so require less oxygen to fully combust.
carbohydrates
- heat of combustion: 16kj g-1
- made form elements carbon, hydrogen and oxygen
- usually polymers of glucose
- during digestion, enzymes in out saliva ans small intestine break down starch into glucose
- this glucose is then transported to our cells where respiration can occur
protein
- heat of combustion: 17kj g-1
- proteins are realy used for energy as they have so many other important roles within the body
- protein will be used as a last resort
fats and oils
- heat of combustion: 37
- higher energy value due to degree that they can be oxidised and can release energy
- triglycerides - large non-polar molecules with three log hydrocarbon chains attached to a glycerol molecule
- digestion breaks down fats which can then be oxidised, releasing energy.
cellular respiration
- organism convert glucose into energy
- glucose is oxidised into carbon dioxide
- C6H12O6 + 6O2 → 6H2O + 6CO2
- exothermic
photosynthesis
- plants convert light energy into chemical energy in the form of glucose
- light is absorbed by chlorophyll which is then used to split water into hydrogen and oxygen ions
- the hydrogen ions are used to built carbohydrates
6CO2 + H20 → C6H12O6 + 6O2 - endothermic
exothermic reaction
- reactions that release energy
- will feel form
- energy of products is more than reactants
- negative ΔH
endothermic reactions
- reactions that absorb heat
- will feel cool
- energy of reactants is more than products
- positive ΔH
making and breaking bonds
- to break bonds, energy is taken in (endothermic)
- to make bonds, energy is released (exothermic)
ΔH
- change in enthalpy of reactants and products
- ΔH = energy of products - energy of reactants
activation energy
- the energy required break the bonds of the reactants to the reaction can proceed
combustion reactions
- occur between oxygen and a fuel
- exothermic
complete combustion
- occur when oxygen is in excess
- produces CO2 and H2O
incomplete combustion
- occurs when oxygen is limited
- produces carbon products like CO or C
thermochemical equations
- a balanced equation that includes the enthalpy change of a reaction
determining limiting reactant
- divide mole by the coefficient and the smaller number is the limiting reactant
heat of combustion
the energy released when a specific amount of a substance reacts completelty with oxygen
sustainable/renewable vs unsustainable/non-renewable production of fuels.
methane
renewable - anaerobic digestion of organic matter (biomass) to produce biogas
non-renewable - obtaining methane from extracting natural gas from underground.
hydrogen
renewable - electrolysis of water, PEM, artificial photosynthesis
non-renewable - natural gas
diesel
renewable - transesterification of triglycerides from organic matter
non renewable - fractional distillation of crude oil
ethanol
renewable - fermentation of glucose from organic plant matter
fossil fuels evaluation
advantages
- high energy density making them more efficient
- there is well developed infrastructure
- cheaper energy sources than biofuels
disadvantages
- environmental impact from fracking and drilling
- greenhouse gas emissions
- non renewable
bio fuels evaluation
advantages
- renewable
- generally no net greenhouse gas production
- can be produced from waste
disadvantages
- land use
- limited energy density
- deforestation
- fossil fuels generally required for growing and transporting
- there is limited infrastructure
food sources for the body
- starched broken down into glucose and stored as glycogen
- proteins broken down into amino acids
- lips broken down into fatty acids
- lips have the most energy per gram because they have more C-H bonds which release a significant amount o energy during metabolism. They also contain less oxygen and so are less oxidised that carbohydrates. this means they have more potential energy in their bonds.
- glucose: serves as the primary energy source and is good for short term quick releases of energy
- proteins: the bodies last resort for energy. they are used for growth and repair
- lipids: the bodies secondary source of energy and can serve as a long term energy reserve.
