User:Neurosojourn

When the user exhales into the breathalyzer, any ethyl alcohol present in their breath is oxidized to acetic acid at the anode:

CH3CH2OH(g) + 4OH-(aq) -> HC2H3O2(g) + 3H2O(l) + 4e-

At the cathode, oxygen gas from the atmosphere is reduced:

O2(g) + 2H2O(l) + 4e- -> 4OH-

The overall reaction, then, is the oxidation of ethyl alcohol to acetic acid and water.

CH3CH2OH(g) + O2(g) -> HC2H3O2(g) + H2O(l)