18
Electrochemistry II:
Balancing Equations
The basic principles discussed at the beginning of Chapter 17 (in connection
with the construction of simple electrochemical cells) are exactly the ones used
to write and balance chemical equations for electron-transfer reactions. These
principles also enable you to predict whether or not a given electron-transfer
reaction will actually take place.
Let us review these principles.
1. Every electron-transfer reaction may be considered to be composed of
two half-reactions, with each half-reaction written in the form
ne~ + oxidizing agent «=* reducing agent
2. Electron-transfer half-reactions may be listed in order of decreasing
tendency for the reducing agents to give up electrons, as in Table 17-1.
3. In any electron-transfer reaction, there must be the same number of
electrons gained by the oxidizing agent as are lost by the reducing
agent.
4. An electron-transfer reaction will occur spontaneously only if the reducing half-reaction lies above the oxidizing half-reaction in a table
such as Table 17-1. This results in a positive £° e ii, a negative AG°, and