# 23.4: Electrical Potential

The voltmeter doesn't measure volts directly; it measures electric current flow. But don't worry - current flow and voltage can be directly related to one another. The first meters were called galvanometers and they used basic laws of electricity to determine voltage. They were heavy and hard to work with, but got the job done. The first multimeters were developed in the 1920's, but true portability had to wait until printed circuits and transistors replaced the cumbersome wires and vacuum tubes.

## Electrical Potential

Electrical potential is a measurement of the ability of a voltaic cell to produce an electric current. Electrical potential is typically measured in volts $$\left( \text{V} \right)$$. The voltage that is produced by a given voltaic cell is the electrical potential difference between the two half-cells. It is not possible to measure the electrical potential difference between the two half-cells. It is not possible to measure the electrical potential of an isolated half-cell.For example, if only a zinc half-cell were constructed, no complete redox reaction can occur and so no electrical potential can be measured. It is only when another half-cell is combined with the zinc half-cell that an electrical potential difference, or voltage, can be measured.

The electrical potential of a cell results from a competition for electrons. In a zinc-copper voltaic cell, it is the copper (II) ions that will be reduced to copper metal. That is because the $$\ce{Cu^{2+}}$$ ions have a greater attraction for electrons than the $$\ce{Zn^{2+}}$$ ions in the other half-cell. Instead, the zinc metal is oxidized. The reduction potential is a measure of the tendency of a given half-reaction to occur as a reduction in an electrochemical cell. In a given voltaic cell, the half-cell that has the greater reduction potential is the one in which reduction will occur. In the half-cell with the lower reduction potential, oxidation will occur. The cell potential $$\left( E_\text{cell} \right)$$ is the difference in reduction potential between the two half-cells in an electrochemical cell.

## Summary

• Definitions for types of electrical potential are given.

## Contributors

• CK-12 Foundation by Sharon Bewick, Richard Parsons, Therese Forsythe, Shonna Robinson, and Jean Dupon.