Cracking is a chemical reaction which produces smaller hydrocarbons, including alkanes and akenes. This process allows large hydrocarbons (which aren't that useful) to be broken down into smaller, more useful hydrocarbon molecules.
Fractions containing large hydrocarbon molecules are heated to vaporise them.
They are then either:
- passed over a hot catalyst
- mixed with steam at a very high temperature
- General formula is CnH2n - General formula is CnH2n+2
- End in -ene (eg. propene) - End in -ane (eg. propane)
- Have at least one double bond - Have NO double bonds
- Unsaturated - Saturated
Monomer: One molecule that can bond with another molecule exactly the same to make a polymer.
Polymer: Lot's of monomers joined together.
Polymerisation: The process where monomers join together to make a polymer.
Monounsaturated: Alkenes which only have one double bond.
Polyunsaturated: Alkenes which have more than one double bond.
Alkenes can act as monomers because they are unsaturated (they have at least one double bond).
Polymers and their uses
Polymers have different properties so they have different uses.
Polythene has properties that make it useful to manufacture plastic bags and bottles.
Polypropene has different properties to polythene and can be used to make crates and ropes.
Polychloroethene is used to make water pipes and insulation on electricity cables as the properties are suited this way.
Polymers are also unreactive and this is good for storing food and chemicals safely.
However, there are some environmental and ethical problems that surround the world of manufacturing polymers...
Problems with polymers
Although polymers have advantages such as being very versatile, they also come with their disadvantages...
- Polymers are difficult to dispose of because they are non biodegradable. Scientists have figured out that it's possible to include substances such as cornstarch that cause the polymer to break down more quickly.
- Polymers are obtained from non-reneable resources (crude oil). New methods have been created to recycle polymers.
- Many people believe that the land should be used to grow food for those living in developing countries, NOT to grow cornstarch to make our polymers more biodegradable.
- Recycling polymers is expensive and it takes time to do.
The formula for ethanol is
H ----- C ----- C ---- O ---- H
This is the displayed formula for ethanol
There are two ways in which we can make ethanol. They are fermentation and the ethene and steam method. Over 90% of the world's ethanol is made through fermentation.
The ethene and steam method:
- Ethene is the only product.
- It is a continuous process - as long as there is ethene and steam, you will carry on making ethanol.
- It is very efficient but it's slow and you need to eet certain conditions to make it.
- However, ethene is obtained from crude oil, which is a NON-RENEWABLE resource.
- CO2 is waste product.
- It is a batch and stop process but it is a very quick method.
- Even though the process is quick, the ethanol still needs purifying as you need to get rid of the dead yeast.
- Making ethanol hrough fermentation is renewable.