Summary
Highlights
Electrochemistry involves reactions that produce or consume free electrons, specifically oxidation-reduction (redox) reactions. These reactions can generate a flow of electrons through a conductor, which can do work. The strength of this electron 'push or pull' is called electrical potential, or voltage. High voltage means each electron can do more work.
Redox reactions are best understood as half-reactions: one where electrons are released (oxidation) and another where they are accepted (reduction). An alkaline battery, for example, involves the oxidation of elemental zinc to zinc 2+ ions and the reduction of manganese 4+ to manganese 3+. To harness this energy, batteries isolate these half-reactions in a cathode and anode, allowing electrons to flow through an external circuit.
Alkaline batteries are a type of galvanic cell, which converts chemical energy from a redox reaction into electrical energy. Another example demonstrates how metal atoms are consumed at the anode and deposited at the cathode. A salt bridge completes the circuit by allowing ion flow between the half-cells.
To determine the voltage a reaction can generate, we use standard reduction potentials, which are measured at standard conditions and indicate the tendency of a substance to be reduced. These potentials are relative to the reduction of hydrogen ions, which is set at zero. To find the overall cell potential, the reduction potential of the oxidized species is reversed (oxidation potential) and added to the reduction potential of the reduced species.
A positive standard cell potential indicates a spontaneous reaction, making it suitable for batteries which need to release energy. Non-spontaneous reactions, like electroplating (e.g., chroming a car bumper), require an external electric current to proceed. This process is called electrolysis and occurs in an electrolytic cell, where electricity is used to break down molecules and facilitate deposition.
Electrolysis has various applications beyond electroplating, including coating jewelry, refining metals, separating metal ion mixtures, and converting water into hydrogen and oxygen gas. Electrochemistry plays a significant role in our daily lives, powering devices and enabling industrial processes.