Ethene is produced by cracking long-chain hydrocarbons. Ethene can then be used to make poly(ethene). Describe how poly(ethene) is formed from ethene and explain why ethene, rather than ethane, must be used as the monomer.

Poly(ethene) is produced by addition polymerisation: many ethene molecules (monomers) join together to give a long chain polymer.

In addition polymerisation the carbon–carbon double bond of each ethene opens, forming new C–C single bonds and linking the monomers together. No other small molecules are lost or released – the only product is the polymer.

Ethene must be used because it is unsaturated and contains a C=C double bond that can open and react. Ethane is saturated, has only C–H bonds and no double bond, so it cannot open up or link with other monomers and therefore cannot undergo addition polymerisation.