Potentially Confusing: Potentials in Electrochemistry

A potential quantifies the capacity of a system to do work. A simple example is from mechanics: by lifting a weight, its potential energy increases. When the weight is dropped, that potential energy is converted into kinetic energy. Applying the concept of potential to electrochemical systems can be surprisingly confusing. Table 1 shows some “potentials” used in electrochemistry and their different units. To start, let us consider a voltage measured with a voltmeter for a given system. Analog voltmeters operate by passing a small current through a calibrated resistor and wire coil, generating a small magnetic field, and thus deflecting a needle attached to a fixed magnet. The current passed through the resistor, which causes needle deflection, is proportional to the voltage. This voltage, however, is not the electric potential difference of the system. Electric potential φ is the line integral of the electric field E⃗ along a path from a reference point (often at infinite distance from the system) to a given position: