Electrolytic Cells

Terms and Formulae

Terms

Anode - The electrode that is the source of the negative charge, designated by a minus sign (-); this electrode is the site of oxidation.

Cathode - The electrode that is the source of positive charge, designated by a plus sign (+); this electrode is the site of reduction.

Cell Potential - The overall electrical potential of an electrochemical cell. It is the sum of the reduction potential of the cathode and the oxidation potential of the anode.

Current - Charge flow per unit time. I(current)=dQ/dt.

Electrochemistry - The study of the exchange between electrical and chemical energy.

Electrode - A conducting material placed in physical contact with a half-reaction on which the electron transfers in the redox reaction take place.

Electrolysis - A reaction that consumes electrical energy to split molecules apart.

Electrolytic Cell - A cell that consumes electrical energy to drive a non-spontaneous redox reaction.

Electroplating - The deposition of a solid material onto an electrode, almost always the cathode.

Electrorefining - Process by which materials, usually metals, are purified by means of an electrolytic cell. The anode is the impure metal and the cathode is a very pure sample of the metal.

emf - Electromotive force, i.e. a potential.

Galvanic Cell - An electrochemical cell with a positive cell potential that allows that chemical energy to be converted into electrical energy.

Half-Cell - A half-reaction and its electrode; it is half of a galvanic cell.

Half-Reaction - Either an oxidation or a reduction reaction; it represents half of the redox reaction.

Hess's Law - The sum of the state functions of a series of reactions is the same as the state function for the overall sum of the reactions.

Line Notation - A shorthand way of describing an electrochemical cell without drawing a picture.

Oxidation - The loss of an electron from a species (an increase in its oxidation number).

Oxidation Number - A conceptual bookkeeping numbering system that allows us to track the number electrons transferred during a redox reaction.

Oxidation Potential - The potential of a half-reaction written as an oxidation reaction, it is the opposite sign of the same reaction written as a reduction.

Oxidizing Agent - A reactant in a redox reaction that accepts an electron from the oxidized species. The oxidizing agent is reduced.

Potentiometer - A device that measures electrical potential.

Reaction Quotient - Similar to the form of an equilibrium constant, the reaction quotient is the ratio of the product of the each product in a reaction raised to its stoichiometric power divided by the product of each reactant raised to its stoichiometric power from the balanced equation.

Redox - A reaction involving the transfer of one or more electrons from the reducing agent to the oxidizing agent.

Reducing Agent - A reactant in a redox reaction that donates an electron to the reduced species. The reducing agent is oxidized.

Reduction - The gain of an electron by a species (a decrease in oxidation number).

Reduction Potential - Arbitrarily setting the potential of the standard hydrogen electrode, SHE, to zero, all other half reactions are measured by their power to reduce hydrogen. The voltage given by the construction of a galvanic cell between the SHE and the redu ction of interest gives the standard reduction potential of that reduction.

Standard State - An arbitrarily defined set of conditions--273K, 1atm for gasses, or 1M for solutions.

Work - Force over a distance.