Electrochemistry is the branch of chemistry that studies the relationship between electrical quantities and chemical reactions, particularly oxidation and reduction. Oxidation is the loss of electrons from a substance, whereas reduction refers to the gain of electrons. A substance with a strong electron affinity is called an oxidizing agent (oxidant), and a reducing agent (reductant) is a species that donates electrons. Oxidation and reduction processes are pivotal to electrochemical reactions, which can be further understood through half-reactions.

When electrons flow through an electric circuit, the measured current and cell voltage can reveal information about the type of reaction. During an electrochemical reaction, the current is proportional to the reaction rate, whereas the voltage is proportional to the free energy change for the reaction. According to Ohm's law, the current is inversely proportional to the resistance of the circuit and directly proportional to the applied potential. This means electrochemical experiments can determine the free energy change and reaction rates by varying potential or current. Electrochemical methods involve inexpensive instruments that provide an advantage over other analytical techniques.