Redox Reactions

  • Created by: Zoe
  • Created on: 14-05-13 15:21


  • Redox reactions are all around and even inside us, for example, repsiration and photosynthesis.
  • Redox Reactions are reactions that involve both oxidation and reduction
  • Oxidation is the loss of electrons from an atom or ion
  • Reduction is the gain of electrons from an atom or ion.







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  • In a redox reaction one atom, ion or molecule will gain electrons from the one that lost it
  • Oxidising agent oxidise other chemicals so they themselves are reduced, they are electron acceptors
  • Reducing agent reduces other chemicals so they themselves are oxidised as they lose electrons, they are electron donors
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Half Equations

  • Half equations show the loss or gain of electrons by one chemical
  • Half equations show what chemical is oxidised and which is reduced.
  • The electron will appear on the left of the equation when a chemical is reduced and on the right of the equation if oxidised. An easy way to remember this is to think there are a reduced number of left handers in the world.
  • Half equations only show half the story, they show how each chemical is effected within the Redox Reaction
  • Spectator Ions- Ions that take no part in the reaction, they are unchanged through the reaction they simple "watch" the reaction take place.
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Combining Half equations

  • When you are given two half-equations you will need to join them together.
  • The aim is to make the same number of electrons equal the same as each other.

How to combine the half equations

  • Step 1: Write the two half equations
  • Step 2: Take a note of how many electrons are lost or gained in each half equations and multiply either the one or both equations to make them both have the same number of electrons in their equations
  • Step 3: Now multiply the number of products and reactants in each equation by the number that you multiplied the electrons with.
  • Step 4: Now combine the equations together and cancel out the electrons as the number of electrons should be the same in each equation.
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Oxidation States

  • An oxidation state is the number of electrons needed to be gained or lost to make a neutral atom.
  • Oxidation states help to work out how oxidized or how reduced something is. It is similar to the charge on the ions, except that it is used for covalent compounds.

Working out oxidation states


  • Elements always have an oxidation state of 0
  • In a compound the sum of the oxidation numbers equals zero
  • In an ion, the sum of the oxidation numbers equals the charge
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