Organic Chemistry
Fractional Distillation
Hydrocarbons
Uses and Cracking of Crude Oil
Alkenes and their Reactions
Bonding in polymers
Definition: A compound made up of Hydrogen & Carbon atoms only
Alkanes: Simplest type of hydrocarbon
CnH2n+2
The alkanes are a homologous series - a group of organic compounds that react in a similar way
Alkanes are saturated compounds - each carbon atom forms four single covalent bonds
The alkanes are: methane, ethane, propane, butane (Mice Eat Peanut Butter)
Properties of hydrocarbons -
The shorter the carbon chain, the more runny the hydrocarbon is (the less viscous it is)
The shorter the carbon chain, the more volatile the hydrocarbon is (ie it turns into a gas at a lower temperature)
The shorter the carbon chain the more flammable the hydrocarbon is
The complete combustion of any hydrocarbon in oxygen releases lots of energy, the waste products are water vapour and carbon dioxide.
Hydrogen + oxygen -> carbon dioxide + water
During combustion, carbon and hydrogen from hydrocarbon are oxidised. Oxidation is the gain of oxygen
Hydrocarbons can be used as fuels due to the amount of energy they release when they combust completely
How it works:
- oil is heated until most of it is gas, the gas then enters the fractionating column
- There's a temperature gradient (hot at the bottom then cooler as you go up the column)
- Longer chain hydrocarbons have higher boiling points so they condense back into liquids and drain out of the column early on when they are near the bottom. Shorter hydrocarbons have lower boiling points so they condense and drain out later on, near the top of the column where it is cooler
- In the end you are left with crude oil mixture separated into different fractions, each fraction has a similar number of carbon atoms (so they have similar boiling points)
- Crude oil is formed over millions of years from the remains of plants and animals, mainly plankton, that were buried in mud. Over the years, with high temperature and pressure, the remains turned to crude oil, which can be drilled from the rocks where it is found. Crude oil is a fossil fuel often used for fuels.
Uses:
Fuel for modern transport ie diesel comes from crude oil
some hydrocarbons can be used as feedstock to make new compounds for use in things like polymers
products from crude oil are examples of organic compounds (compounds containing carbon atoms)
What is cracking?
splitting up of long-chain hydrocarbons because short-chain hydrocarbons make good fuels and are in high demand. Cracking produces alkanes and alkenes (used as starting material when making other compounds and can be used to make polymers). Some products of cracking are useful as fuels
Methods of cracking (thermal decomposition reaction)
catalytic cracking
- vaporise (turn to gas) the long chain hydrocarbon
- vapour is passed over hot powdered aluminium oxide catalyst - long chain molecules split on surface of specks of catalyst
steam cracking
- vaporise them, mix hydrocarbons with steam, heat them to a high temperature
Alkenes have at least one double bond between carbon atoms
CnH2n
alkene molecules are unsaturated
Polymers are made up of thousands of small, identical molecules, monomers, which are often alkene molecules
Monomers have double carbon bonds while polymers have single covalent bonds, which are very strong
Polymers are solids at room temperature because they have relatively strong intermolecular forces between the molecules so it takes a lot of energy to separate the molecules.