Question

How can you recognize oxidation reduction reactions?

Answer 1

By a change in formal oxidation number of the participating reactants with respect to the products.

Explanation:

See this old answer for some tips and principles. Any reaction that involves a change in formal oxidation number is a redox reaction. Under this umbrella lies simple combustion reactions of hydrocarbons, e.g.:

`CH_4 + 2O_2 rarr CO_2 + 2H_2O`

We have balanced this directly with no pfaffing about with electron transfer. But we could assign oxidation numbers to the individual atoms, and use the method of half equations:

`"Oxidation (i):"`
`C^(-IV)H_4 +2H_2O rarr C^(+IV)O_2 +8H^+ + 8e^-`

`"Reduction (ii):"`
`O_2 +4H^(+) +4e^(-)rarr 2H_2O^(-II)`

And we add `"(i)" + "(ii)"xx2:`

`""^(-IV)CH_4 +2O_2^0 rarr ""^(-IV)CO_2^(-II)+2H_2^(-II)O`

To give the original equation as required.