cracking and alkenes

what is cracking?

cracking is the process by which longer chain hydrocarbons are split into shorter and more useful hydrocarbons - generally, cracking results in an alkane and an alkene

why are the products of cracking useful?

shorter hydrocarbons make better fuels and shorter alkenes can also be used as feedstock for the petrochemical industry to make polymers and detergents

what type of reaction is cracking an example of?

cracking is a thermal decomposition reaction - e.g. breaking down molecules by heating them

what catalyst is used in catalytic cracking?

hot powdered aluminium oxide

outline how catalytic cracking works

long chain alkanes are heated until they vaporise into a gas, then the gaseous alkanes are passed over a hot aluminium oxide catalyst which breaks the long chain alkanes into a shorter chain alkane and an alkene

how is steam cracking different to catalytic cracking?

steam cracking is different because there is no catalyst involved - instead, the vaporised long chain alkane is mixed with steam at very high temperatures

why is there not an alkene called methene?

the prefix ‘meth’ in methene would indicate there is only one carbon atom, and so there couldn’t be a carbon-carbon double bond, meaning the molecule wouldn’t be an alkene

what is the general formula for alkenes?

C_nH_2n

what colour change occurs when you add bromine water to alkenes?

orangey brown to colourless