Which of the following best describes chemical action that establishes a difference of potential?

The description of chemical action that establishes a difference of potential is best exemplified by a storage battery or dry cell. These devices function based on electrochemical reactions that occur within their cells. In a battery, chemical reactions between the electrolyte and the electrodes produce a buildup of electrons at one terminal, creating an electric charge. This charge difference ultimately results in a potential difference, or voltage, that can be harnessed to power electrical devices.

In the case of electric generators, while they do produce voltage, the mechanism relies on electromagnetic induction rather than chemical action. Heating the junction of metals involves a phenomenon known as the thermoelectric effect, which is related to temperature differences creating a voltage but does not pertain to chemical actions specifically. A circuit with unloaded voltage refers to a situation where there is potential present without any current flow due to a lack of load, which does not involve chemical reactions establishing voltage. Thus, the storage battery or dry cell stands out as the best option to describe the process where chemical action leads to a difference of potential.