is done by adding , and/or to either side of the reaction until both atoms and charges are balanced. Consider the half reaction below: PbO2 -> PbO , and can be used to balance the charges and atoms in basic conditions, as long as it is assumed that the reaction is in water. 2e- + H2O + PbO2 -> PbO + 2OH- Again consider the half reaction below: PbO2 -> PbO , and can be used to balance the charges and atoms in acidic conditions, as long as it is assumed that the reaction is in water. 2e- + 2H+ + PbO2 -> PbO + H2O Notice that both sides are both charge balanced and atom balanced. Often there will be both and present in acidic and basic conditions but that the resulting reaction of the two ions will yield water, (shown below): H+ + OH- -> H2O See also Electrode potential Standard electrode potential (data page) References Electrochemistry