Topic 6 National Chemistry Summary Notes. Fuels. Fuels and Combustion

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1 Topic 6 National Chemistry Summary Notes Fuels LI 1 Fuels and Combustion Coal, oil, gas and wood can all be used as fuels. These fuels have energy-rich chemical bonds which were created using the energy from the SUN. The energy is released when the fuel burns. A FUEL is a substance which gives out ENERGY when it burns. Any compound with STORED energy can be considered as a fuel. When fuels burn they react with OXYGEN. This may also be referred to as OXIDATION. Scientists use the word COMBUSTION to describe the process of burning. Combustion is an example of an exothermic reaction i.e. one which releases energy. e.g. the combustion of carbon: C (s) + O 2 (g) CO 2 (g) (balanced) An ENDOTHERMIC reaction is one in which energy is taken in. LI 2 The Fire Triangle The three things needed for burning are a fuel, oxygen and heat. These make up the three sides of the fire triangle. If you take away one side of the triangle, it will collapse. This means that if you deprive a fire of either, fuel, oxygen or heat, then it will go out. 1

2 LI 3 Fossil Fuels Coal, oil and natural gas are the three main fuels used in the UK today. They are called the FOSSIL FUELS because they were formed from once LIVING THINGS. Fossil fuels such as oil and gas are examples of HYDROCARBON compounds with minor impurities (coal is mostly just carbon). Hydrocarbons are compounds made up of hydrogen and carbon only. Even although there are large amounts of coal, oil and gas in the world today, they will eventually run out. For this reason fossil fuels are called FINITE resources because supplies are limited. Formation of Coal The formation of coal started around 300 million years ago. It is made from dead plants and fern like trees that became buried in swampy land. Pressure and temperature gradually made coal. Formation of Oil & Natural Gas Crude oil and natural gas came from microscopic sea animals and plants that died and became covered by sediment. Again pressure and temperature over millions of years changed the once living organisms into crude oil and natural gas. Uses of Fossil Fuels The fossil fuels are a useful reserve of fuels and are used to satisfy the demands of an energy-dependent world e.g. Electricity: The most common use of fossil fuels is the generation of electricity. Fossil fuels like coal run most of the power plants in the world that generate electricity. Transportation: Most modes of transport are powered by coal and petrol. Though hybrid and electric vehicles have made inroads into our lives, fossil fuels still power millions of vehicles. Industrial production: Fossil fuels, especially coal and oil, power most of the industries throughout the world. Kitchens: Nearly one-third of world's population uses fossil fuels like coal and biomass, (such as wood and dung) for cooking and heating. Heating: During winters, fossil fuels serve as excellent heat generators. 2

3 LI 4 Fractional Distillation of Crude Oil The oil which comes out our oil wells is a black, sticky liquid with a very unpleasant smell. It is called CRUDE OIL. It contains a rich mixture of valuable chemicals called HYDROCARBONS. The problem for chemists is how to separate the hydrocarbons in crude oil. However, each hydrocarbon has its own BOILING POINT. If the crude oil is slowly heated then each different hydrocarbon will boil and turn into a GAS at different temperatures. The different gases can be collected separately. When the gases cool they CONDENSE and turn into LIQUIDS. Each separate liquid is called a FRACTION.A fraction is defined as a mixture of hydrocarbons with similar boiling points. This whole process is called FRACTIONAL DISTILLATION. The first fractions which are obtained consist of GASES then they become light coloured LIQUIDS and after that darker in colour liquids and thicker. The final fraction which is left is known as BITUMEN RESIDUE and is the sticky material used for building roads. Fractional Distillation in the Lab The set-up below shows how fractional distillation can be carried out in the lab. 3

4 The purpose of the air condenser is to cool the gases into liquids to allow for collection. The first fractions are volatile, light in colour, runny and highly flammable. The later fractions are darker in colour, viscous and not so flammable. definitions - volatile = flammability = viscosity = evaporates easily how easily a substance catches fire how thick a liquid is Fraction Boiling Range (ºC) Number of Carbon Atoms per Molecule Colour Viscosity Flammability Speed of Evaporation Gases Gases LOW RUNNY LIQUID Catches fire easily FAST Petrol Clear, light coloured liquid Naphtha Kerosene (paraffin) Pale yellow Catches fire with difficulty Gas oils (diesel) Dark yellow Residue > 350 > 25 Dark Brown HIGHLY VISCOUS (very thick) Does not catch fire SLOW 4

5 Uses of Fractions FRACTION Refinery Gas Petrol Naphtha Kerosene Diesel (gas oils) Lubricating oils Bitumen USE Cooking, heating Car fuel Chemicals e.g. plastics, solvents Jet fuel Heavy transport, some cars Engine oil, candle wax Building roads, roofing The following saying can help us to remember the order and names of the fractions obtained from the fractional distillation of crude oil. Giant Planes Need Kerosine During Our Boarding G A S E S P E T R O L N A P T H A K E R O S I N E D I E S E L O I L S B I T U M E N 5

6 Fractional Distillation in Industry Liquefied petroleum gas Chemicals Fractions decreasing in density and boiling point Petrol for vehicles Jet fuel, paraffin for heating and lighting Diesel fuels Crude oil Lubricating oils, waxes and polishes Fractions increasing in density and boiling point Fuels for ships, factories and central heating Bitumen for roads and roofing 6

7 LI 5 Properties of Crude Oil Fractions The fractions obtained from crude oil have different properties because they contain hydrocarbons of different sizes. The simplest way to think about the size of a hydrocarbon is to count the number of carbon atoms in the molecule. a) Boiling Points The first fractions that are distilled have low boiling points. This is because they consist of small molecules. There are small forces of attraction that exist between molecules. These forces are bigger and stronger for large molecules. It takes more energy to separate large molecules and therefore larger molecules have higher boiling points. b) Viscosity (thickness) The fractions containing bigger molecules have a higher viscosity. This is because they are made of long chains of atoms which tend to get tangled up and clump together. c) Flammability Small hydrocarbons are more flammable than larger molecules i.e. they catch fire more easily. This is because small molecules can react more quickly with oxygen in the air. d) Ease of Evaporation Small molecules evaporate more easily than larger molecules since they have much lower boiling points. 7

8 LI 6 Combustion of a Hydrocarbon This apparatus can be used to show the combustion products of a hydrocarbon. The burning wax candle produces gases which are drawn through the apparatus by the pump. u-tube Results 1. The limewater turns milky indicating the presence of carbon dioxide gas. 2. The drops of condensation in the u-tube boil at 100ºC and freeze at 0⁰C. This indicates the presence of water. Complete Combustion hydrocarbon + oxygen carbon dioxide + water e.g. complete combustion of methane gas - CH 4 CH 4 (g) + O 2 (g) CO 2 (g) + H 2 O (l) (unbalanced) CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O (l) (balanced) Hydrocarbons burn in a plentiful supply of oxygen to produce CARBON DIOXIDE and WATER. This is called COMPLETE COMBUSTION. 8

9 LI 7 Incomplete combustion Often when a fuel burns there is not enough oxygen to produce carbon dioxide gas (CO 2 ). Instead, the gas carbon monoxide, (CO) is formed. Carbon monoxide is a poisonous gas. In large amounts it can kill by destroying the blood s ability to carry oxygen. hydrocarbon + limited carbon monoxide + water oxygen In a limited supply of oxygen, hydrocarbons burn to produce carbon monoxide gas. This is called INCOMPLETE COMBUSTION. LI 8 Catalytic Converters In car engines, catalytic converters can be used to minimise the output of carbon monoxide. This device fits on to the exhausts of cars and converts harmful gases into harmless ones. However, they have no beneficial effect on carbon dioxide levels which contribute to GLOBAL WARMING. LI 9 Fuels and Pollution POLLUTANT MAIN SOURCE EFFECT Carbon monoxide Vehicle engines and industry Sulphur dioxide Burning fossil fuels in power stations Hydrocarbons Burning fuels in vehicles and factories Oxides of nitrogen (NO x ) Vehicle engines Poisonous Forms acid rain Irritating, toxic compounds formed in air Forms acid rain Lead compounds Used to be added to petrol to make it burn more smoothly Toxic and can cause brain damage 9

10 LI 10 Global Warming and the Greenhouse Effect The increasing level of carbon dioxide in the atmosphere is a cause for concern. As the amount of carbon dioxide in the atmosphere increases more of the suns energy is retained. This causes the average temperature of the earth s surface to rise. This is known as the GREENHOUSE EFECT. Scientists still argue about the effect this will have but it is thought some parts of the world will warm up by around 4⁰C whilst other parts may cool down. This may well cause flooding in certain areas due to an increase in the levels of rivers and seas. Burning fuels for heating, for cars and other vehicles and for making electricity in power stations all produces carbon dioxide which adds to the greenhouse effect. How much CO 2 does your lifestyle emit each year? 10

11 LI 11 Reducing Carbon Dioxide Emissions Alternative Energy Sources Fossil fuels are in short supply and will eventually run out, for this reason they are called NON RENEWABLE sources of energy. Other methods of generating electricity need to be developed. These include using the sun s energy, wind, water and wave action. These methods provide an unlimited supply and they will not run out. They are called RENEWABLE or ALTERNATIVE ENERGY sources. RENEWABLE ENERGY SOURCE ADVANTAGES DISADVANTAGES Hydroelectric Solar Wind Wave 11

12 Biofuels Biofuels are considered a viable alternative to fossil fuels. Many different varieties exist and they vary significantly. All biofuels and bio-based products come from biomass, a term that covers all living or recently living biological material which can be used as fuel or for industrial production. Examples include wood, corn, sugarcane, and manure. Biofuels can be separated into three basic categories: A. ETHANOL: primarily used in cars, ethanol is a type of alcohol and is most commonly made from corn or sugarcane. B. BIODIESEL: a substitute for diesel fuel, which is used mostly in lorries and trucks but also in an increasing number of diesel cars. Most commonly made from soybeans. C. OTHER BIOMASS: mostly used for generation of electricity or heat. Examples: burning wood chips to boil water and create steam, which spins turbines and creates electricity; collecting methane from manure piles to generate heat or electricity ADVANTAGES Made from renewable sources so will not run out Safer for the environment if they get spilled BIOFUELS DISADVANTAGES Land not always available to grow crops Decreased access to food Less pollution compared to regular fuels Some biofuels are more corrosive than petrol and damage engines Cheaper than regular fuels since plants are cheaper than oil Do not contribute to increased levels of CO 2. 12

13 LI 12 Carbon Capture Carbon capture and storage (CCS) is the process of capturing waste carbon dioxide (CO 2 ) from large point sources, such as fossil fuel power plants, transporting it to a storage site, and depositing it where it will not enter the atmosphere, normally deep underground. The aim is to prevent the release of large quantities of CO 2 into the atmosphere from fossil fuel use in power generation and other industries. Although CO 2 has been injected into geological formations for several decades for various purposes, the long term storage of CO 2 is a relatively new concept. 13

14 Topic 6 Pupil Self Evaluation Number Learning Intention Success Criteria 1 I will found out about fuels and combustion 2 I will find out what makes up the three sides of the fire triangle 3 I will find out about the fossil fuels, how they were formed and their uses 4 I will find out how crude oil is separated into different fractions by the process of fractional distillation State the definition of a fuel Give examples of fuels State that energy is released when fuels burn State that combustion is an exothermic reaction Write a combustion word/formula equation Define the terms exothermic and endothermic Draw the fire triangle State what happens when one side of the fire triangle is removed State the three fossil fuels are coal, oil and natural gas Describe the formation of the fossil fuels State that the fossil fuels are finite resources State that oil and gas are hydrocarbon compounds with minor impurities. Give examples of uses of the fossil fuels Describe how hydrocarbons in crude oil are separated by their difference in boiling point. 14

15 Describe how fractional distillation is carried out in the lab and in industry State the names of the different fractions Give uses for fractions 5 I will find out about the properties of the different fractions obtained from crude oil 6 I will find out what the combustion products of a hydrocarbon are by experimentation 7 I will find out what the products of incomplete combustion of a hydrocarbon are 8 I will find out the purpose of fitting catalytic converters to cars Describe the different properties of fractions in terms of carbon chain length, colour, viscosity, flammability and ease of evaporation Explain why properties of fractions change as molecules increase in size State the products of complete combustion of a hydrocarbon as carbon dioxide and water Describe the chemical test for carbon dioxide and water Write a formula/word equation for complete combustion of a hydrocarbon State that carbon monoxide and water are the products of incomplete combustion of a hydrocarbon State that carbon monoxide is a poisonous gas Describe the effect carbon monoxide has on the body State that catalytic converters change harmful gases into harmless gases 15

16 9 I will find out about pollutants, their sources and environmental effects 10 I will find out about global warming and its environmental effects 11 I will find out about alternative energy sources including biofuels State that fitting a catalytic converter does not have a beneficial effect on carbon dioxide levels in the atmosphere. Give examples of pollutants from fuels State the source of the pollutant and describe its effect on the environment and our health Explain why the temperature of the earth is increasing Give examples of the effects of global warming Give examples of renewable energy State advantages and disadvantages of renewable energy 12 I will find out about carbon capture Describe what is meant by carbon capture Explain why this would be beneficial to the environment 16