What is direct current causing a chemical reaction referred to as?

The correct term for direct current causing a chemical reaction is known as "galvanic." This term originates from the work of Luigi Galvani, who discovered that electrical currents could induce chemical reactions in conductive mediums, particularly in electrolytic solutions. In galvanic processes, the direct current facilitates the movement of ions in a solution, leading to reactions such as electroplating or electrolysis, where chemical changes occur at the electrodes as a result of the current flow.

The other terms do not accurately describe this phenomenon. "Thermal" relates to heat energy and does not specifically address currents or electrochemical reactions. "Electromagnetic" pertains to the interaction of electric and magnetic fields, which while relevant in broader electrical contexts, does not specifically denote the chemical reactions triggered by direct current. "Chemical," while it may seem relevant, is too broad and does not specifically imply the involvement of direct current in producing chemical changes. Thus, "galvanic" is the precise term that encapsulates the concept of direct current instigating a chemical reaction.