Question

what is half reaction method.... with example...

Answer 1

First, divide the equation into two halves; an oxidation half-reaction and reduction-reaction by grouping appropriate species. Third, balance the oxygen atoms using water molecules . (The hydrogen and oxygen atoms are already balanced; hence, skip this step also.

Answer 2

Balancing Redox Reactions Using the Half Reaction Method

Many redox reactions occur in aqueous solutions or suspensions. In this medium most of the reactants and products exist as charged species (ions) and their reaction is often affected by the pH of the medium. The following provides examples of how these equations may be balanced systematically. The method that is used is called the ion-electron or "half-reaction" method.

Example 1 -- Balancing Redox Reactions Which Occur in Acidic Solution

Organic compounds, called alcohols, are readily oxidized by acidic solutions of dichromate ions. The following reaction, written in net ionic form, records this change. The oxidation states of each atom in each compound is listed in order to identify the species that are oxidized and reduced, respectively.

Cr2O72-  +  C2H6O     Cr3+       +       C2H4O 
dichromate  ethanol              chromium(III)  acetaldehyde