IB Chemistry R3.2 Electron Transfer Reactions Key Definitions

The anode is the electrode in an electrochemical cell where oxidation occurs. Electrons are produced at the anode and flow into the external circuit.

The cathode is the electrode in an electrochemical cell where reduction occurs. Electrons arrive at the cathode from the external circuit.

An electrochemical cell is a device that uses redox (reduction-oxidation) reactions to either produce or consume electrical energy.

Electrodes are solid surfaces where the redox reactions occur

Electrolysis uses electrical energy to drive non-spontaneous redox reactions.

An electrolytic cell is a device that uses electrical energy to force a non-spontaneous redox reaction to occur.

Electroplating is a process that uses an electrolytic cell to coat an object (usually the cathode) with a thin layer of metal.

Gibbs free energy ($\Delta G$) is a thermodynamic property that determines whether a chemical reaction is spontaneous under constant pressure and temperature.

A half-equation focuses on one part of a redox reaction: either the oxidation or reduction process.

Hydrogenation is a chemical reaction where hydrogen ($H_2$) is added to an unsaturated compound. This reaction is classified as a reduction because the molecule gains hydrogen atoms, reducing its degree of unsaturation.

Oxidation is the loss of electrons by an atom or ion. It can also refer to the gain of oxygen or the loss of hydrogen.

The oxidation state (or oxidation number) is a numerical value assigned to an atom in a compound. It is the hypothetical charge the atom would have if every bond were treated as fully ionic (bonding electrons assigned to the more electronegative atom).

An oxidizing agent is a species that accepts electrons from another species in a redox reaction. It is itself reduced in the process.

The reactivity series ranks metals in order of their tendency to lose electrons and be oxidised. Metals higher in the series displace those below them from ionic solutions.

A redox reaction is a chemical reaction in which electrons are transferred from one species to another. Oxidation and reduction always occur simultaneously.

A reducing agent is a species that donates electrons to another species in a redox reaction. It is itself oxidized in the process.

Reduction is defined as the gain of electrons by an atom or ion. It can also refer to the loss of oxygen or the gain of hydrogen.

Reduction in organic chemistry refers to the gain of hydrogen atoms or the loss of oxygen atoms in a molecule.

The salt bridge is a tube or porous material filled with an ionic solution (e.g., KNO₃ or Na₂SO₄). It allows ions to flow between the two half-cells, maintaining electrical neutrality and completing the circuit.

A secondary cell is a rechargeable electrochemical cell whose redox reactions can be reversed by applying an external voltage, restoring the reactants and allowing the cell to be reused.

The standard cell potential, denoted as $E^\circ_{\text{cell}}$, is the voltage produced by an electrochemical cell under standard conditions.

A voltaic (galvanic) cell is an electrochemical cell that converts the energy released by a spontaneous redox reaction into electrical energy.