chemistry

• the definition of a fuel, including the distinction between fossil fuels (coal, natural gas, petrol) and biofuels (biogas, bioethanol, biodiesel) with reference to their renewability (ability of a resource to be replaced by natural processes within a relatively short period of time)

  carbon base fuels
• ¡A substance that burns in air or oxygen to release useful energy¡Fossil fuels (non-renewable) and biofuels (renewable)¡Renewable – energy sources that can be produced faster than they are used

  whats a fuel
• fossil fuels are non-renewable resources that have been formed from the remains of dead plants and animals over millions of years.
• what is a carbon based fuel
• Biofuels are renewable sources of energy made from living organisms such as crops or waste products.
• what is a non carbon based fuel
• The main types of carbon based fuels include coal, oil/petroleum, and natural gas.
• what is an example of a non carbon based fuel
• ¡Made up of carbon, oxygen, water and traces of other elements¡80% extracted through open-cut mining¡Brown coal¡23-60 million years¡Low in sulfur and nitrogen¡High water content¡6-12 MJ g-1¡Black coal¡145-299 millions years¡Lower water content¡More polluting¡17-24 MJ g-1
• ¡Lightest of hydrocarbons produced¡Composition is typically 80% methane, 10% ethane, 4% propane, 2% butane, other gases (N2, He)¡Less dense than air¡Explosive¡Odourless (odour added to detect leaks)¡Coal seam gas (CSG)¡Extracted by fracking¡Deep wells drilled into underground coal deposits¡Water and chemical injected at high pressures¡Rocks are cracked to desorb methane from coal¡Environmental concerns with polluting local water sources

  Natural gas
• ¡Refined from crude oil (petroleum) through fractional distillation¡Include petrol (gasoline), diesel (petrodiesel), kerosene, liquefied petroleum gas (LPG), aviation fuel¡Petrol¡Mixture of alkanes, alkenes and cyclic hydrocarbons (4-12 carbons)¡Energy content 44-46 MJ g-1¡Diesel¡Mixtures of hydrocarbons (12-24 carbons)¡Comparison to petrol¡Similar energy content¡Higher density¡Combusts more efficiently

  Petrochemical fuels
• ¡Renewable, carbon-based energy source formed in a short period of time¡Made from waste plant and animal matter¡Three most common are biogas, biodiesel and bioethanol

  biofuels
• ¡May contain up to 65% methane¡Produced from fermentation of organic matter (e.g. animal manure)¡Methane from biogas (biomethane)¡90% produced through “upgrading” -  removal of CO2 and H2¡Also produced by breaking down biomass at high temperatures in oxygen-deficient environment

  biogas
• ¡Made from plant oils and animal fats¡Transesterification reaction¡Conversion of one ester (triglyceride) to another ester (biodiesel)¡Fats and oils (triglycerides) react with methanol¡Heat and a catalyst required (KOH or NaOH)¡Biodiesel and glycerol products

  Biodiesel
• ¡Ethanol produced from plants (e.g. sugarcane) and used as an alternative to petrol¡Obtained by fermenting sugar from by-products of sugar production¡E10 fuel contains 10% bioethanol¡Reduces pollutant emissions¡Presence of oxygen assists in complete combustion of fuel¡Costly¡More carbon neutral¡Requires land for crops which could have been used for food production
• ¡production of bioethanol by the fermentation of glucose,

    C6H12O6(aq) → 2C2H5OH(l) + 2CO2(g)

    and subsequent distillation to produce a more sustainable transport   fuel
• The production of bioethanol ¡Fermentation¡Biochemical process¡Yeast digests fermentable sugars (monosaccharides) to make energy¡C6H12O6(aq) → 2C2H5OH(l) + 2CO2(g)¡Distillation¡Separates bioethanol from water after fermentation¡Mixture heated to just above BP (78.3 oC)¡Ethanol vaporises, is cooled and condensed back into a liquid¡Expensive¡94 %v/v
• Energy output ¡Varies for different fuels based on type and percentage of combustible material in fuel¡Biofuels are partially oxidised¡Increased water content will reduce energy output as water absorbs heat¡Most commercial fuels are not pure so KJ g-1 more appropriate than KJ mol-1¡Energy transformations are not 100 per cent efficient. This is because heat is also produced
• ¡Sustainable energy – energy that meets present needs without compromising the ability of future generations to meet their own needs¡Fossil fuels (non-renewable) and biofuels (renewable)¡Renewable – energy sources that can be produced faster than they are used¡Non-renewable – energy sources that are consumed faster than they are being formed¡Known reserves of fossil fuels¡Oil and gas – 50 years supplyCoal – 100 years supply
• ¡Fossil fuels¡SO2, NOx, CO and particulate pollutants¡Release of stored carbon as CO2¡Biofuels¡Close to net zero carbon emissions (carbon neutral)¡Greenhouse effect – natural process of warming Earth’s surface¡Greenhouse gases - CO2, CH4, N2O, O3, H2O¡Enhanced greenhouse effect – effect of increasing concentrations of GG from human activity¡Climate change – changes in various measures of climate over a long period of time
• ¡comparison of exothermic and endothermic reactions, with reference to bond making and bond breaking, including enthalpy changes (∆H) measured in kJ, molar enthalpy changes measured in kJ mol-1 and enthalpy changes for mixtures measured in kJ g-1, and their representations in energy profile diagrams
• ¡Thermochemistry – the branch of chemistry concerned with the quantities of heat evolved or absorbed in chemical reactions¡All chemical reactions involve energy changes¡Types of energy¡Mechanical¡Thermal (heat)¡Chemical¡Light¡Sound¡Electrical¡Gravitational¡Nuclear
• ¡Chemical energy is stored in every atom, molecule or ion (potential + kinetic energy)¡Attraction and repulsion between protons and electrons¡Attraction and repulsion between atoms in a molecule¡Motion of electrons¡Movement of the atoms¡Total energy stored¡Enthalpy / H / heat content¡Change in enthalpy¡ΔH  / heat of reaction / heat of solution / heat of neutralization / heat of vaporization / heat of combustion
• ¡Exothermic¡describes a chemical reaction in which energy is released to the surroundings¡ΔH is negative¡Endothermic¡describes a chemical reaction in which energy is absorbed from the surroundings¡ΔH is positive¡Enthalpy change (ΔH) is measured at Standard Laboratory Conditions (SLC) in kilojoules (kJ)¡Pure substances kJ mol-1Mixtures kJ g-1
• ¡combustion (complete and incomplete) reactions of fuels as exothermic reactions: the writing of balanced thermochemical equations, including states, for the complete and incomplete combustion of organic molecules using experimental data and data tables
• ¡Limiting reactant¡Completely consumed in the reaction¡Limits the quantity of products formed according to mole ratio in equation¡In combustion reactions, usually the fuel is the limiting reactant with excess oxygen¡Use mole ratios of reactants in equation to determine limiting and excess reactants¡Use moles of limiting reactant and ΔH  to determine total energy released or absorbed in reaction
• ¡Redox reactions as fuels are oxidised¡Complete combustion¡Excess oxygen¡At SLC, products are H2O(l) and CO2(g)¡Incomplete combustion¡Limiting oxygen¡At SLC, products are H2O(l) and CO2(g) / CO(g) / C(s)¡¡
• ¡fuel sources for the body measured in kJ g-1: carbohydrates, proteins and lipids (fats and oils)
• ¡Participate in chemical reactions (metabolism)¡Energy content from food depends on the amount of carbohydrates, proteins, fats and oils¡Carbohydrates 16 kJ g-1¡Proteins 17 kJ g-1Fats and oils 37 kJ g-1
• ¡Collectively called lipids or triglycerides (formed by a condensation reaction between glycerol and 3 fatty acids)¡Fats are solid at room temperature¡Oils are liquid at room temperature¡Contain carbon, hydrogen and oxygen¡80% of the body’s energy storage in adipose (fatty) tissue¡Oxidised in an exothermic reaction e.g. linolenic acid, a polyunsaturated omega-6 fatty acid
• ¡ protein Hydrolysed into amino acids by enzymes and HCl (in stomach)¡Amino acids used to make other proteins required in body e.g. enzymes, keratin, haemoglobin¡Excess amino acids are converted to glucose for energy, and waste excreted as urea.
• ¡Carbohydrates Monosaccharides¡Simple sugars¡Building blocks of all carbohydrates¡eg. glucose¡Disaccharides¡Two monosaccharides bonded together¡eg. sucrose, maltose¡Polysaccharides¡More than 10 monosaccharides bonded together¡eg. starch, cellulose¡Cellulose is indigestible (dietary fibre) as humans do not have enzyme required to hydrolysed it¡Excess glucose in diet can be stored in liver as glycogen
• ¡photosynthesis as the process that converts light energy into chemical energy and as a source of glucose and oxygen for respiration in living things:

    6CO2(g) + 6H2O(l) → C6H12O6(aq)+ 6O2(g)
• photosynthesis¡Endothermic redox reaction¡Enthalpy change is approximate due to other products forming¡Efficiency of photosynthesis depends on;¡Type of plant or organism¡Amount and type of chlorophyll¡Other photosynthetic pigment, minerals and nutrients available¡Maximum efficiency (sunlight à chemical energy) is 26%¡Only 1-2% energy stored in plants due to some wavelengths of light being absorbed or reflected, and plant processes
• ¡oxidation of glucose as the primary carbohydrate energy source, including the balanced equation for cellular respiration:

    C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l)
• Cellular respiration¡Exothermic redox reaction¡Complicated series of biochemical reactions¡Aerobic respiration¡Oxygen required¡Occurs in cells of all living organisms¡Provides energy for essential processes of life
• Cellular respiration ¡Anaerobic respiration¡No oxygen present¡eg. high demand for fast energy during exercise¡Product is lactic acid which is oxidised later¡Lactic acid causes soreness in muscles¡Also occurs in plant cells (fermentation)¡eg. yeast for bread-making, and ethanol to make wine