A galvanic cell is a device in which a chemical reaction occurs in such a way that it generates energy. The conductors of the cell, metals in the activity series, are called the electrodes; they are connected to the external circuit. For a galvanic cell to function in must be in an electrolyte solution. The electrolyte is the substance which in solution conducts electricity and is connect by a salt bridge.
In the diagram below the copper nitrate, silver nitrate and potassium nitrate solutions are electrolyte solutions. The salt bridge in this diagram is a U tube filled with KNO3. The salt bridge in a galvanic cell is used to make electrical contact between the two solutions and therefore must contain a conducting substance; in this case KNO3. The electrodes in the diagram below are Cu (Cu electrode) and Ag (Ag electrode) and give off two half reactions which result in the electron transfer that gives the electrical current; this electricity again being produced by a chemical reaction from the electrodes and electrolytes. The electrons flow out of the Cu electrode and into the voltmeter (external circuit) then into the Ag electrode. The half reactions are as followed:
Cu(s) → Cu2+(aq)
+ 2e-
Ag+(aq) + e-
→ Ag(s)
In these half reaction the Cu is losing electrons, therefore oxidising and the Ag is gaining electrons, therefore reducing. When combining these two half reaction, you get the full redox reaction of:
Cu(s) + 2Ag+(aq)→
Cu2+(aq) + 2Ag(s)
In the diagram above the reason the Cu is oxidising to Cu ions and Ag ions are reducing to Ag metal is due to their position on the activity series for metals.
The activity series of metals is a listing of metals in order from left to right of decreasing reactivity. This means that metals to the left are more likely to oxidise or decrease and give up electrons to the metals on the right. Below is the activity series of metals.
K Na Li Ba Ca Mg Al Zn Fe Sn Pb (H) Cu Ag Pt Au
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