Reversible reactions

• In a reversible reaction there is a forward reaction
• And a backward reaction
• Both take place at the same time
• As a result there is an equilibrium between the reagents and their products
• That is at some point during the reaction process the amounts of both the reagents and their products remain constant because new products are made while the product breaks back into its reagents
• In a reversible reaction the products of the reaction can be converted back into the reagents under suitable conditions
• For example if two chemicals A and B can be combined together and react to form chemicals C and D
• In a reversible reaction C and D can be turned back into A and B
• In addition to reversible chemical changes there are physical changes
• Physical changes are reversible
• For example water can be turned into steam if heated but it turns back into liquid water if cooled
• This can be shown using the equation:
• \text{water}\xrightleftharpoons[cool]{heat}\text{vapour}
• The double arrows show that this is a reversible change
• Similarly iodine if heated sublimates:
• \text{solid iodine}\rightleftharpoons \text{iodine vapour}
• Candle wax also melts when heated and solidifies when cooled

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