Expressing a reaction in terms of half-reactions

Example 5.2 ) Expressing a reaction in terms of half-reactions 

Express the oxidation of nicotinamide adenine dinucleotide, which participates in aerobic metabolism, to NAD (Atlas N4) by oxygen, when the latter is reduced to HjOj, in aqueous solution as the difference of two reduction half-reactions. The overall reaction is NADH(aq) -F 02(g) -F H (aq) — NAD (aq)-FH202(aq). 

Strategy To express a reaction as the difference of two reduction halfreactions, identify one reactant species that undergoes reduction and its corresponding reduction product, then write the half-reaction for this process. To find the second half-reaction, subtract the first half-reaction from 

Solutbn Oxygen is reduced to H2O2, so one half-reaction is 

Subtraction of this half-reaction from the overall equation gives 

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