Walking through a Redox Reaction

In a redox reaction, the total charge is always balanced. In the simplest of cases, one atom gains electrons, while another loses electrons. As with the galvanic cell, the reaction can be divided into two half reactions, one of oxidation and one of reduction. These half reactions can make balancing redox equations easier when many elements are involved. 

Consider the following equation where the numbers above the chemical symbols represent the oxidation states of the elements. 

Hydrogen and oxygen have the same oxidation state on both sides of the equation (1 and -2, respectively), yet both manganese and chlorine change (for example, the oxidation state of Mn decreases by 2, so it gained two electrons Cl ions loses one electron). However, this isn t an even exchange of electrons as written. For this to balance out, there need to be two atoms of Cl (so two electrons are lost to equal the two electrons gained by Mn). Thus the equation looks like  

At this point, the electron exchange is balanced however, there are four Cl atoms on the right and only two on the left. Finally, changing the coefficient of HCl to 4 and H2O to 2 balances out the elements. 

In the following example, however, the redox equation only lists the ions important to the reaction (spectator ions, or ions not involved in the actual reaction, are not listed). 

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