Why do the following reactions proceed differently? `Pb_(3)O_(4)+8HClrarr3PbCl_(2)+Cl_(2)+4H_(2)O` and `Pb_(3)O_(3)+4HNO_(3)rarr 2Pb(NO_(3))_(2)+PbO_(2)+2H_(2)O`

Explanation

`Pb_(3)O_(4)` is actually a mixed oxide of PbO and `PbO_(2)`. In `PbO_(2)` lead is present in +4 oxidatioin state and in PbO it is +2. `PbO_(2)` thus can act as an oxidant (oxidising agent) and, therefore, can oxidise `Cl^(-)` ion of HCl into chlorine PbO is a basic oxide. The reaction is
`Pb_(3)O_(4)+8HCl to 3PbCl_(2)+Cl_(2)+4H_(2)O`
can be splitted into two reactions namely:
`2PbO+4HCl to 2PbCl_(2)+2H_(2)O` (acid-base reaction)
`Pb overset(+4)(O_(2))+4 overset(-1)(HCl) to Pb overset(+2)(Cl_(3))+ underset("redox reaction") overset(0)(Cl_(2))+2H_(2)O`
`HNO_(3)` being strong oxidising agent, the reaction between PbO and `HNO_(3)` does not take place. The acid base reaction can be possible between PbO and `HNO_(3)` as follows: `2PbO+4HNO_(3) to 2Pb(NO_(3))_(2)+2H_(2)O`