How can you recognize oxidation reduction reactions?

1 Answer
anor277
Feb 5, 2017

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.

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