CHAPTER 4. ELECTROCHEMICAL REACTIONS 4.4
- --2+
2+
2+
2+
2+
Zn2+ions in solutionzinc metalconcentration of electrons on metal surfaceFigure 4.1: Zinc loses electrons to form positiveions in solution. The electrons accu-
mulate on the metal surface.
Zn2+(aq) + 2e−� Zn (s)(NOTE: By convention,the ions are written on the left hand side of the equation)
In the zinc half cell, theequilibrium lies far to the left because the zinc loses electrons
easily to form Zn2+ions. We can also say that the zinc is oxidised and that it is a strong
reducing agent.
At the copper electrode, a similar process takesplace. The difference though is that
copper is not as reactiveas zinc and so it does not form ions as easily. This means that
the build up of electrons on the copper electrode is less (figure 4.2).
2+
2+Cu2+ions in solutioncopper metalconcentration of electrons on metal surfaceFigure 4.2: Zinc loses electrons to form positiveions in solution. The electrons accu-
mulate on the metal surface.
The equilibrium reactionis shown like this:
Cu2+(aq) + 2e−� Cu (s)The equation lies far to the right because most of the copper is present as copper metal
rather than as Cu2+ions. In this half reaction, the Cu2+ions are reduced.