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Half-reaction

 

 
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A half reaction is either the oxidation or reduction reaction component of a redox reaction. A half reaction is obtained by considering the change in oxidation state
Oxidation state

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical Electrical charge that an atom would have if all bonds to atoms of different elements were 100% Ionic bond....
s of individual substances involved in the redox reaction.

Consider the reaction below:

Cl2 + 2Fe2+ ? 2Cl- + 2Fe3+


The two elements involved, iron
Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
 and chlorine
Chlorine

Chlorine...
, each change oxidation state; iron from 2+ to 3+, chlorine from 0 to 1-.






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Encyclopedia


A half reaction is either the oxidation or reduction reaction component of a redox reaction. A half reaction is obtained by considering the change in oxidation state
Oxidation state

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical Electrical charge that an atom would have if all bonds to atoms of different elements were 100% Ionic bond....
s of individual substances involved in the redox reaction.

Consider the reaction below:

Cl2 + 2Fe2+ ? 2Cl- + 2Fe3+


The two elements involved, iron
Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
 and chlorine
Chlorine

Chlorine...
, each change oxidation state; iron from 2+ to 3+, chlorine from 0 to 1-. There are then effectively two half-reactions occurring. These changes can be represented in formulas by inserting appropriate electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
s into each half-reaction:

Fe2+ ? Fe3+ + e-
Cl2 + 2e- ? 2Cl-


In the same way given two half-reactions it is possible, with knowledge of appropriate electrode potentials, to arrive at the full (original) reaction.

See also

  • Electrode potential
  • Standard electrode potential (data page)
    Standard electrode potential (data page)

    The standard electrode potentials are electrode potentials of half cells at equilibrium. They can be used to determine the potential of an electrochemical cell or galvanic cell, or a position of equilibrium for an electrochemical reaction, or a direction in which an electrochemical reaction can proceed....