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Terms and Formulae


Anode  -  The electrode that is the source of the negative charge, designated by a minus sign (-); this electrode is the site of oxidation.
Battery  -  A galvanic cell or cells connected in series with a constant amount of reagents. A battery stores energy in the form of chemical potential energy, which is released as electrical energy.
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.
Concentration Cell  -  A galvanic cell that has two compositionally equivalent half-cells of differing concentrations. One can calculate the potential developed by such a cell using the Nernst Equation.
Current  -  Flow of charge 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.
Fuel Cell  -  A galvanic cell with a constant flow of reagents in and products out used for the prodction of a constant supply of energy. Whereas batteries have a finite lifetime of useful energy production, fuel cells are only limited in their duration of energy production by the ammount of available fuel reagents.
Galvanic Cell  -  An electrochemical cell with a positive cell potential that allows 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.
Half-Reaction Method  -  The set of rules that have been developed to aid in balancing redox reactions. See Balancing Redox Reactions for details.
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. This system is further described in Line Notation.
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 of electrons transferred during a redox reaction. The rules for determining the oxidation number of a species are discussed in Galvanic Cells, Oxidation State.
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.
pH Meter  -  A concentration cell that places a known concentration of acid in the meter's electrode. When that probe is dipped into a solution of unknown acid concentration, a potential develops due to the differences in concentration which can be calculated by the Nernst Equation. From that potential, the meter calculates the concentration of the unknown acid and, therefore, its pH.
Porous Disk  -  A disk placed between two half-reactions allowing ion flow between half-reactions without mixing the reactions. The mixing of the two cells would cause a short in the circuit.
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 reduction of interest gives the standard reduction potential of that reduction.
Salt Bridge  -  A tube plugged with pourous material at either end (usually cotton) filled with a gel allowing ion flow between half-reactions without mixing the reactions. The actual mixing of the two cells would cause a short in the circuit.
Standard State  -  An arbitrarily defined set of conditions--273K, 1atm for gasses, or 1M for solutions.
Work  -  Force over a distance.


Adding Cell Potentials Eo cell = Eo 1 + Eo 2
Nernst Equation E = Eo - (RT/nF) ln Q

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