5.1 Cracking
Alkane
Shorter chained hydrocarbons are more useful than longer chained ones because longer chained hydrocarbon do not flow as well and are harder to ignite. Cracking is a process that breaks down less useful longer chained hydrocarbons, like tar, into shorter more useful hydrocarbons. The shorter hydrocarbons are usually alkanes and alkenes (explained below). Some of the smaller hydrocarbons are used as fuel and others are used to make polymers.
Cracking is a thermal decomposition reaction, which is the breaking down of molecules by adding heat. Cracking follows the follow steps:
An alkane is a saturated hydrogen carbon, meaning that every covalent bond from a carbon atom is joined to another carbon atom or to a hydrogen atom. All the bonds are single bonds.
Shorter chained hydrocarbons are more useful than longer chained ones because longer chained hydrocarbon do not flow as well and are harder to ignite. Cracking is a process that breaks down less useful longer chained hydrocarbons, like tar, into shorter more useful hydrocarbons. The shorter hydrocarbons are usually alkanes and alkenes (explained below). Some of the smaller hydrocarbons are used as fuel and others are used to make polymers.
Cracking is a thermal decomposition reaction, which is the breaking down of molecules by adding heat. Cracking follows the follow steps:
- Heat up the long chained hydrocarbon so that they turn into a gas (vaporise)
- Pass the vaporised longer hydrocarbons over a powdered catalyst (sometimes aluminium) or mixed with steam at a very high temperatures
- Thermal decomposition occurs as longer chained hydrocarbons split up into smaller chained hydrocarbons (both alkanes and alkenes)
An alkane is a saturated hydrogen carbon, meaning that every covalent bond from a carbon atom is joined to another carbon atom or to a hydrogen atom. All the bonds are single bonds.
Alkene
Alkenes are hydrocarbons that are unsaturated because they have a double bond and therefore can make more bonds; a double bond can be broken and form a bond with a hydrogen atom. Alkenes have the general formula CnH2n. We draw a double bond with two lines. It looks like an equal sign (=). Let’s take the example of ethene and propene
Alkenes are hydrocarbons that are unsaturated because they have a double bond and therefore can make more bonds; a double bond can be broken and form a bond with a hydrogen atom. Alkenes have the general formula CnH2n. We draw a double bond with two lines. It looks like an equal sign (=). Let’s take the example of ethene and propene
Hydorcarbon; Alkene or Alkane?
The easy way to know whether a hydrocarbon is saturated (alkane) or unsaturated (an alkene) is to look at the name. All alkanes have the ending “ane” and all alkenes have the ending “ene”.
The easy way to know whether a hydrocarbon is saturated (alkane) or unsaturated (an alkene) is to look at the name. All alkanes have the ending “ane” and all alkenes have the ending “ene”.
Testing if a Substance is an Alkene
You can test if a substance is an alkene by adding it to bromine water. Bromine water is orange and will change its colour to colourless when an alkene is added. This is because the double bond has opened and formed bonds with the bromine.
You can test if a substance is an alkene by adding it to bromine water. Bromine water is orange and will change its colour to colourless when an alkene is added. This is because the double bond has opened and formed bonds with the bromine.