Question

What is the meaning of a positive sign for half cell potential?

Answer 1

Hint: We know that the galvanic cell consists of two half cells which are joined by a salt bridge that allows the passing of ions between the two sides to maintain electroneutrality. The conversion of chemical energy of a spontaneous reaction into electrical energy takes place in the galvanic cell.

Complete step by step solution:
Let's understand the working of a galvanic cell. We know that redox (oxidation and reduction) reactions take place in galvanic cells. Both oxidation and reduction reaction takes place in two different parts of the galvanic cell. These two portions of the galvanic cell are termed as half cells. Each half cell is composed of a metallic electrode that is dipped in an electrolyte and the connection of the two half cells are done by a wire (metallic) through a switch and voltmeter externally. The electrolytes in the two half cells are connected by a salt bridge internally. In some cases, both the half cells are immersed in the same electrolyte. In that case, there is no need for a salt bridge.

Let's discuss the cell potential. In a galvanic cell, the two electrodes' potential difference gives the cell potential. It is expressed in volts. The formula to calculate cell potential is,

$E_{\mathrm{c}\mathrm{e}\mathrm{l}\mathrm{l}}=E_{\mathrm{r}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t}}-E_{\mathrm{l}\mathrm{e}\mathrm{f}\mathrm{t}}$

Now, come to the question. The potential developed at each half cell is termed as half cell potential. If half cell potential has positive sign then it indicates the non-spontaneous reduction reaction.

Note: The development of potential difference between electrolyte and electrodes of half cell is termed as potential difference. If the concentration of all species involved in a half cell is unity, then the electrode potential is termed as standard electrode potential.