3.2 Alkanes

• Alkanes have a general formula of CnH2n+2, where n is the number of carbons.
• Alkanes are saturated hydrocarbons, meaning they have no double bonds in their molecules.
• Alkanes are hydrocarbons that contain hydrogen and carbon only.
• Alkanes are found in crude oil, which is a mixture of different lengths of hydrocarbons.
• Fractional distillation is a practical technique used to separate these different hydrocarbon lengths.
• In fractional distillation, the crude oil is vaporized and enters a column, rising through trays.
• The longest hydrocarbons, which don't vaporize, run to the bottom of the column and collect in the slurry.
• Oil is refined into fractions such as gasoline, diesel oil, fuel oil, kerosene, and petrol.
• Alkanes burn completely with oxygen, producing carbon dioxide and water.
• Gas is used in LPG, stove gas, petrol, and kerosene.
• Diesel oil is used to fuel diesel trains and ships.
• Cracking is a process used in the petrochemicals industry to produce lighter fractions from heavy fractions.
• Bitumen and asphalt are used in roofing and tarmac.
• Fuel oil is used in ships and power stations.
• Catalytic cracking uses a catalyst to produce mainly aromatic hydrocarbons useful in fuels for vehicles.
• Thermal cracking uses heat and high temperature and pressure to produce mainly alkenes.
• The vapor rises when it rises, condenses at different temperatures, and then these different temperatures correspond to different hydrocarbon lengths.
• Photochemical smog is caused by the burning of fossil fuels such as alkanes, which occurs in the lowest level of the atmosphere.
• Complete combustion of butane produces the same number of molecules of carbon dioxide as it consumes.
• Incomplete combustion occurs when there is a limited supply of oxygen, producing carbon monoxide and other products.
• Carbon monoxide is poisonous and prevents hemoglobin from binding oxygen, leading to an oxygen deficiency.
• Carbon monoxide can be removed from the blood by using a catalytic converter.
• Burning fuels either produce complete combustion or mainly produce carbon dioxide and water.
• Global warming is caused by the increase in amounts of carbon dioxide in the atmosphere.
• Burning fossil fuels, such as alkanes, produces carbon dioxide, a greenhouse gas that traps heat from the Sun.
• Photochemical smog is formed when hydrocarbons and nitrogen dioxide mix, creating a harmful substance known as ozone.
• The shorter chain hydrocarbons come off at the top of the column, have the lowest boiling point, and are still gases at this point.
• The longer chain hydrocarbons, which condense to a liquid, are collected on trays at a higher temperature.
• These fractions, which are collected from the column, are known as the fractions of fractional distillation.
• Propagation in a free radical reaction is where a radical meets with a non-radical, they react, and new radicals are formed.
• Initiation in a free radical reaction involves the production of radicals, normally using visible light or ultraviolet, and these are called photochemical reactions.
• Free radical reactions contain three main stages: initiation, propagation, and termination.
• Oxides of nitrogen do the same.
• Sulphur dioxide can be removed from things like chimneys and factories using a process called wet scrubbing, where we use an arc I to neutralize the sulfur dioxide in the flue gases.
• Acid rain is caused by burning fossil fuels and releasing sulphur dioxide and nitrous oxides of nitrogen.
• Photochemical smog is a respiratory system harm caused by nitrogen oxides and oxides of nitrogen, which are caused by nitrogen and oxygen reacting under high pressure and temperature in the engine.
• Catalytic converters can help remove or reduce the amount of unburned hydrocarbons that haven't quite burnt in the engine and they can prevent the oxides of nitrogen from going into the atmosphere because they can react them and try and reduce the levels of them.
• Ozone is toxic and should not be present in the lower atmosphere.
• Oxides of nitrogen are caused by nitrogen and oxygen reacting under high pressure and temperature in the engine.
• These new radicals then go on to react with other non-radicals, which is why this reaction is called a chain reaction because it literally just keeps going and going.