organic chemistry

• a hydrocarbon is any compound that is formed from carbon and hydrogen atoms only
• hydrocarbons are used as fuels due to the amount of energy they release when they combust
• alkanes are the simplest type of hydrocarbon. they have C-C single bonds and are saturated compounds. they are part of a homologous series
• a saturated compound contains carbon atoms that form 4 single covalent bonds each
• some examples of alkanes are methane, ethane, propane, and butane.
• methane displayed formula

  A) CH4

  
• ethane displayed formula

  A) C2H6

  
• propane displayed formula

  A) C3H8

  
• butane displayed formula

  A) C4H10

  
• formula for alkanes is CnH2n+2
• a homologous series is a group of organic compounds that react in a similar way
• if the length of the carbon chain changes, the properties of the hydrocarbons change
• hydrocarbons with shorter carbons chains are less viscous(more fluid) and are more volatile, meaning they have a lower boiling point. they are also more flammable
• complete combustion is when all the hydrogen in a fuel is burned. it takes place when there is plenty of oxygen and releases lots of energy. the products of complete combustion are CO2 and water vapour
• during combustion, the carbon and hydrogen from the hydrocarbon are oxidised, meaning they gain oxygen
• oil is the fuel for most modern transport. diesel, kerosene, heavy fuel oil and LPG all come from crude oil
• fractional distillation is used to separate mixtures of liquids with different boiling points
• Process of fractional distillation:
• Oil is heated until most turns to gas. The gases enter the fractionating column and the liquid is drained off
• In the column, there is a temperature gradient. It is hot at the bottom and gets cooler as you go up
• The longer hydrocarbons have higher boiling points. They condense back into liquids and drain out of the column early on near the bottom
• The shorter hydrocarbons have lower boiling points. They condense and drain much later on near the top where it's cooler
• You end up with crude oil separated into different fractions. Each fraction contains a mixture of hydrocarbons that all contain a similar number of carbons so they all have a similar boiling point
• crude oil is formed from the remains of plants and animals that died millions of years ago and got buried in mud. it is a mixture of different hydrocarbons, most of which are alkanes. the different compounds are separated by fractional distillation
• the petrochemical industry uses some of the hydrocarbons in crude oil as a feedstock to make new compounds for use in polymers, solvents, lubricants or detergents
• organic compounds are those that contain carbon. the products you get from crude oil are organic compounds. the reason you get such a wide variety of products is because the carbon atoms can bond together to form a homologous series
• cracking turns longer alkane molecules into smaller, more useful ones. it produces alkenes as well as alkanes. it is a thermal decomposition reaction, meaning it breaks molecules down by heating them
• catalytic cracking -heat the long chain hydrocarbons to turn them into gas (vaporised) -the vapour is passed over a hot powdered aluminium oxide catalyst -the long chain molecules then split apart on the surface of the specks of the catalyst
• steam cracking -vaporise the hydrocarbons -mix them with steam -heat to a very high temperature
• alkenes have C=C double bonds between 2 of the carbon atoms in the chain. they have fewer hydrogens compared to alkanes containing the same number of carbons. the C=C double bonds can open up to make single bonds allowing 2 carbon atoms to bond with other atoms, this makes alkenes more reactive than alkanes
• some examples of alkanes are ethene, propene, butene, and pentene.
• ethene displayed formula

  A) C2H4

  
• propene displayed formula

  A) C3H6

  
• butene displayed formula

  A) C4H8

  
• Pentene displayed formula

  A) C5H10

  
• the formula for alkenes is CnH2n
• incomplete combustion occurs when there's not enough oxygen for complete combustion to occur. less energy is released and it results in a yellow smoky flame. the products of incomplete combustion are water vapour and carbon dioxide but also carbon and carbon monoxide which is toxic gas
• the equation for incomplete combustion is alkane + oxygen = carbon + carbon monoxide + carbon dioxide + water vapour (+energy)
• a functional group is a group of atoms in a molecule that determine how that molecule reacts
• alcohols are formed by alkenes reacting with steam and water is added across the double bond