Properties, Production and Chemical Reactions of Ethene (Ethylene) Chemistry Tutorial

Key Concepts

• Ethene is also known as ethylene.
• Ethene (ethylene) has the molecular formula C₂H₄
• Ethene has the structural formulae shown below:

  Lewis Structure	Valence Structure	2-Dimensional Structural Formula	Condensed Structural Formula (semi-structural formula)
  H ..   H .. C :: C .. H   .. H	H |   H | C = C | H   | H	H   H   \   /     C = C     /   \   H   H	H2C=CH2

• Ethene (ethylene) belongs to the alkene homologous series.

Properties of Ethene (ethylene)

• colourless gas at room temperature and pressure

  ⚛ Melting point = -169°C

  ⚛ Boiling point = -104°C

• slightly sweet smell
• flammable
• non-polar molecule

  ⚛ soluble in non-polar solvents

  ⚛ insoluble in polar solvents like water

• reactive: the active site is the double bond

  For example, ethene readily undergoes addition reactions

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Reactions of Ethene (ethylene)

Ethene (ethylene) undergoes complete combustion in excess oxygen to produce carbon dioxide and water.

Ethene (ethylene) undergoes addition reactions with:

• halogens
• haloalkanes (alkyl halides)
• hydrogen (H₂)
• water (H₂O)

The chemical reactions of ethene (ethylene) are summarised in the table below:

Uses of Ethene (ethylene)

Ethene, ethylene, is an important chemical in the production of other chemicals.
Some of the uses of ethene (ethylene) in industry are given in the table below:

Production of Polythene (polyethylene)	nCH2=CH2	catalyst → high pressure	(CH2-CH2)n
Production of Industrial Alcohol (ethanol)	CH2=CH2	(1) H2SO4 → (2)H2O	CH3-CH2OH
Production of 1,2-ethanediol (ethylene glycol)	CH2=CH2	(1) O2/catalyst → (2) H2O	CH2OH-CH2OH
Production of Styrene styrene can be polymerised to form polystyrene	CH2=CH2	benzene →
Production of chloroethane chloroethane is used to manufacture tetraethyl lead tetraethyl lead is the lead additive in leaded petrol	CH2=CH2 + HCl	→	CH3-CH2Cl
Ethene is also used as a plant hormone to control the ripening and colour development of fruit

Production of Ethene (ethylene)

Ethene can be produced either by:

1. Extraction from natural gas using fractional distillation followed by steam cracking (the technique for converting alkanes to alkenes)(750 - 900°C) followed by liquefaction of the gas (-100°C) and then further fractional distillation

   OR

2. Extraction from crude oil using fractional distillation followed by steam cracking (750 - 900°C) of the naphtha or gas-oil fractions followed by liquefaction of the gas (-100°C) and then further fractional distillation.

The cracking process typically involves endothermic equilibrium reactions such as:

• C₂H₆(g) ⇋ C₂H₄(g) + H₂(g)       ΔH = +138 kJ mol^-1
• C₃H₈(g) ⇋ C₂H₄(g) + CH₄(g)       ΔH = +81 kJ mol^-1

To maximize the rate of the cracking reactions:

• the temperature can be increased so that the gas particles move more quickly and collide more often
• increase the pressure which forces the gas particles closer together and collide more often
• no catalyst is needed to increase the rate of this reaction since the steam provides the required activation energy

To maximize the yield of ethene, by Le Chetalier's Principle:

• increasing the temperature of the reactions favours the formation of products since the reactions are endothermic.
  So increasing the temperature speeds up the rate of the reaction and increases the yield of ethene.
• a decrease in pressure would favour the the formation of products since there are more gaseous product molecules than there are gaseous reactant molecules.
  However, a decrease in pressure would slow down the rate of the reaction. For this reason the pressure is kept at or below atmospheric pressure.
• removing the product will favour the formation of more product thereby increasing the yield of product.
  Equilibrium is therefore never actually achieved (this is not a closed system).