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Types of redox reaction

Redox (reduction-oxidation) reactions are those in which the oxidation states of the reactants change. This occurs because in such reactions, electrons are always transferred between species. Redox reactions take place through either a simple process, such as the burning of carbon in oxygen to yield carbon dioxide (CO₂).

Combination:

Combination reactions "combine" elements to form a chemical compound. As usual, oxidation and reduction occur together.

 H₂ + O₂ → 2 H₂O

The sum of oxidation states in the reactants is equal to that in theproducts: 0 + 0 → (2)(+1) + (-2)

In this equation, both H₂ and O₂ are the molecular forms of their respective elements and therefore their oxidation states are 0. The product is H₂O: the oxidation state is -2 for oxygen and +1 for hydrogen.
Decomposition:

Decomposition reactions are the reverse of combination reactions, meaning they are the breakdown of a chemical compound into its component elements.

 Displacement:

Displacement reactions, also known as replacement reactions, involve compounds and the "replacing" of elements. They occur as single and double replacement reactions.

Cl₂ + 2 NaBr → 2 NaCl + Br₂

Calculation: 0 + [(+1) + (-1) = 0]

In this equation, Cl is reduced and replaces Br, while Br is oxidized.

General equation (double displacement): AB + CD → AD + CB

A double replacement reaction is similar to a single replacement reaction, but involves "replacing" two elements in the reactants with two in the products.

Equation: Fe₂O₃ + 6 HCl → 2 FeCl₃ + 3 H₂O

Combustion:

Combustion reactions always involve oxygen and an organic fuel. In the following image, we see methane combusting to release energy.

Disproportionation: