Redox Reactions

Basics of Redox Reactions:

  • In a redox reaction, one or more electrons are transferred between reactants, causing a change in their oxidation states.
  • Oxidation and reduction reactions always occur simultaneously, a phenomenon known as redox coupling.
  • Oxidation is the loss of electrons, or increase in oxidation state; reduction is the gain of electrons, or decrease in oxidation state.
  • An atom, ion, or molecule that donates an electron in a redox reaction is termed the reducing agent, while the acceptor is termed the oxidising agent.

Oxidation States:

  • The oxidation state of an atom in elemental form (uncombined with other elements) is zero.
  • The sum of oxidation states for all atoms in a neutral molecule or formula ion is equal to its charge.
  • For monatomic ions, the oxidation state equals the charge.
  • In a molecule containing atom A bonded to atom B, A is assigned an oxidation state based on the relative electronegativities of A and B.

Balancing Redox Reactions:

  • Half-reaction method is commonly used to balance complex redox reactions.
  • In half-reaction balancing, the reaction is split into two half-reactions – one for oxidation and one for reduction.
  • Each half reaction is balanced separately and then added to give the final balanced redox reaction.

Redox in Electrochemistry:

  • In electrochemical cells, a redox reaction is split into two half-reactions that occur separately at the two electrodes.
  • The anode is where oxidation takes place, and the cathode is where reduction occurs.
  • The flow of electrons from anode to cathode through an external circuit provides an electrical current.
  • The potential difference between the two electrodes in an electrochemical cell is known as the cell potential or electromotive force (emf).

Redox in Industry:

  • Redox reactions play a key role in processes such as metal extraction, bleaching, and water treatment.
  • For example, aluminum is extracted from its ore (bauxite) using a redox reaction in the Hall-Heroult process.
  • Redox reactions are also at the heart of energy production in fuel cells, batteries, and combustion processes.

Redox in the Environment:

  • Redox reactions play a vital part in natural processes such as photosynthesis, respiration, and nitrogen fixation.
  • Oxidation also plays a role in the corrosion of metals and the ripening of fruit.