FUELS

• is a substance with stored chemical energy than can easily be for use (heat/power) • high energy content→ release a large amount of energy energy use: transport, heating, electricity generation all chemicals contain stored energy but they can’t all be used as fuels

• a fuel is considered non-renewable when it cannot be replenished at the rate at which it is consumed • eg. fossil fuels → coal, crude oil (petroleum), natural gas

• formed from the decomposition of buried dead organisms (plants, animals, microorganisms) • compacted underground w/ high pressure + heat • retains chemical energy accummulated through photosynthesis formation occurs over millions of years

• made from wood and plant material • overtime, water content decreases • carbon content increases • amount of hydrogen and oxygen decreses • presence of water decreases its energy content • black coal - very small amount of water, high carbon content + high amount of potential energy • formed under increased temp and pressure • deeper undergorund

C(s) + O2(g)→CO2(g) energy release: 32kjg^-1 CHEMICAL ENERGY CONVERTED TO ELECTRICITY

• coal is burnt → chemical energy converted to thermal energy • heat from burning → boil water • thermal energy transferred to steam • steam passes through a turbine • thermal energy in steam becomes mechanical energy as the turbine spins • least efficient step • electricity is produced from a generator driven by the turbine • mechanical energy is converted to electrical energy • energy is lost at each step → mostly as heat (30-40% efficiency)

• unrefined liquid extracted from below Earth’s surface • a mixture of hydrocarbon molecules (mostly alkanes) • needs to be separated via fractional distillation to extract smaller fractions that serve as fuel • crude oil itself has no use as a fuel • petrol: includes octane + other alkanes • petrodiesel: includes alkanes that are longer than in petrol

• found in deposits in the earths crust • composed mainly of methane, small amounts of ethane and propane, water sulphur, nitrogen and cvarbon dioxide • extracted via drilling • once a hole has been drilled into the ground, gas will naturally migrate to the surface for capture • found in gas reservoirs trapped between layers of rocks • trapped in shale rock (shale gas) • coal deposits (coal seam gas) • fracking is used to extract natural gas

combustion of natural gas formula: CH4(g) +2O2(g) →CO2(g) +2H2O(g) * gases are used to spin turbines * this generates electrical energy * 55.6kjg^-1 energy released

• derived from plant materials • grains, sugar cane and vegetable waste (oils) • have less impact on the environment than fossil fuels • could be carbon neutral: plant materials used are produced via photosynthesis (removes carbon dioxide from atmosphere (net zero) • the release of carbon dioxide from combustion is offset by the carbon dioxide absorbed by plants through photosynthesis

• produced by fermentation of starches and sugars • accelerated using enzymes • enzymes catalyse the breakdown of these components into sugars (then fermented into ethanol in the absence of oxygen • Bioethanol formation (equation) C6H12O6(aq) → 2CH3CH2OH(aq) + 2CO2(g) • can be blended with petrol for use in motor vehicles • reduces the emission of harmful gases such as oxides of nitrogen

• require land which could be used to grow food • require harsh pre-treatment to break down material • energy content around 38% less than petrol • lower energy content is a result of carbon atoms in ethanol being partly oxdised

• yeasts containing enzymes that catalyse fermentation • starches → sugar • sugar → ethanol + carbon dioxide

• used to separate water from ethanol to obtain a purer product • water falls to the bottom and ethanol is collected from the top • distillation uses the different boiling points of liquid to separate the components in the mixture - the presence of water in bioethanol will reduce its energy content/prevent it from combusting BIOETHANOL IS PRODUCED AS AN AQUEOUS SOLUTION

C2H5OH(l)+3O2(g)⟶2CO2(g)+3H2O(l) • releases 29.6kJg^-1

• formed from anaerobic breakdown of organic waste • anaerobic bacteria involved in the decomposition of organic wastes break complex molecules (carbohydrates and proteins) into smaller molecular compounds like CO2 and methane • small scale electricity generators rather largepower plants • lower efficiency -> biogas has less methane than natural gas

• a mixture of esters • a renewable fuel produced in a reaction between a vegetable oil or an animal fat (trigylcerides) + a small alcohol molecule (methanol) in the presence of a catalyst (KOH) • known as transesterification • the proess of exchanging organic functional groups of an ester with the organic group of an alcohol • used as fuel for diesel engine

• a fuel is renewable if it can be replaced by natural processes within a relatively short period of time) • biofuels - biogas, bioehtanol and biodiesel are renewable • are all produced form organic matter that can be grown in a short period of time

• supplies energy for our bodies • provides materials for growth + repair of tissues • provides materials for the control of body processes humans obtain less energy from food by digestion than the energy released from the direct combustion of food

• carbohydrates (sugars and starch) • lipids (fat and oils) • proteins

• endothermic reaction → energy from sun is required for reaction to proceed • chlorophyll in the leaf assists with the collection of solar energy • glucose moelcules are transported in the sap of a plant to its cells • combine to form polymers starch and cellulose 6CO2(g) + 6H2O (l) → C6H12O6 (aq) + 6O2 (g)

• occurs in the mitochondria in humans • substances from food react w oxygen to release energy required by the cell • exothermic reaction • chemical energyis stored in glucose and is released for use by the body • can be converted to: • thermal energy for warmth • electrical energy in our nerves • chemical energy to produce pther moelcules • mechanical energy in our muscles C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l)

• law of conservation of energy states that energy cannot be created or destroyed • it can change forms • a chemical equation is described as being a system • energy released or absorbed by a system is in the form of thermal energy • can be converted into other types of energy → light, electricity, kinetic

• the total chemical energy of the products is less than the total energy of the reactants • energy is released from the system and into the surroundings • ΔH will be negative • More energy is required to break the bonds in the products than in the reactants. • The products are more chemically stable compared to the reactants. goal of atoms is to be stable IF THE BONDS IN A MOLECULE ARE WEAK, THEN THE CHEMICAL POTENTIAL ENERGY IS HIGH AND STABILITY IS LOW