Half-reaction
Half reactions represent oxidation or reduction in redox processes.
A half reaction (or half-cell reaction) is either the oxidation or reduction component of a redox reaction. It is obtained by considering the change in oxidation states of individual substances involved. Half reactions are used to describe what occurs in an electrochemical cell, such as a Galvanic cell battery at one of the two electrodes, and are often used as a method of balancing redox reactions.
- field
- Chemistry
- known_for
- Representing oxidation or reduction components of redox reactions; balancing redox reactions; describing electrochemical cell processes
Lore & Background
In chemistry, a half reaction is either the oxidation or reduction reaction component of a redox reaction. It is obtained by considering the change in oxidation states of individual substances involved in the redox reaction. Often, the concept of half reactions is used to describe what occurs in an electrochemical cell, such as a Galvanic cell battery at one of the two electrodes. In the case of metal plating and metal stripping, the same half reaction can be written to describe both the metal undergoing oxidation (known as the anode) and the metal undergoing reduction (known as the cathode).
Reader's Guide
Half reactions are key to understanding a variety of chemical processes. They are often used as a method of balancing redox reactions. For oxidation-reduction reactions in acidic conditions, after balancing the atoms and oxidation numbers, H+ ions must be added to balance the hydrogen ions in the half reaction. For oxidation-reduction reactions in basic conditions, after balancing the atoms and oxidation numbers, it must be treated as an acidic solution, and then OH− ions must be added to balance the H+ ions in the half reactions (which would give H2O). The decomposition of a reaction into half reactions is key to understanding a variety of chemical processes, such as showing that a reaction is a redox reaction in which one substance is oxidised and another is reduced. Decomposition is also a way to simplify the balancing of a chemical equation, allowing a chemist to atom balance and charge balance one piece of an equation at a time.
Did You Know?
- A half reaction is either the oxidation or reduction component of a redox reaction.
- In a Galvanic cell, the oxidation half reaction occurs at the anode and the reduction half reaction at the cathode.
- For balancing in basic conditions, the reaction is first treated as acidic, then OH− ions are added to balance H+ ions, yielding H2O.
- The sum of the oxidation half reaction and the reduction half reaction is the overall redox reaction.
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