Terms and Formulae
The electrode that is the source of the negative charge, designated by a
minus sign (-); this electrode is the site of oxidation.
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.
The electrode that is the source of positive charge, designated by a plus
sign (+); this
electrode is the site of reduction.
The overall electrical potential of an electrochemical cell. It is the sum
the reduction potential of the cathode and the oxidation potential
of the anode.
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
Flow of charge per unit time. I(current)=dQ/dt.
The study of the exchange between electrical and chemical energy.
A conducting material placed in physical contact with a half-reaction
on which the electron transfers in the redox reaction take place.
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.
An electrochemical cell with a positive cell potential that allows chemical energy to be converted into electrical energy.
A half-reaction and its electrode; it is half of a galvanic cell.
Either an oxidation or a reduction reaction, it represents half of the
The set of rules that have been developed to aid in balancing redox
reactions. See Balancing Redox Reactions
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.
A shorthand way of describing an electrochemical cell without drawing a
picture. This system is further described in Line
The loss of an electron from a species (an increase in its oxidation
A conceptual bookkeeping numbering system that allows us to track the
number of electrons
transferred during a redox reaction. The rules for determining the
of a species are discussed in Galvanic Cells, Oxidation
The potential of a half-reaction written as an oxidation reaction, it is
the opposite sign of the same reaction written as a reduction.
A reactant in a redox reaction that accepts an electron from the
oxidized species. The oxidizing agent is reduced.
A concentration cell that places a known concentration of acid in the
electrode. When that probe is dipped into a solution of unknown acid
potential develops due to the differences in concentration which can be
calculated by the
From that potential,
calculates the concentration of the unknown acid and, therefore, its pH.
A disk placed between two half-reactions allowing ion flow between
mixing the reactions. The mixing of the two cells would cause a short in
A device that measures electrical potential.
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
A reaction involving the transfer of one or more electrons from the
reducing agent to
the oxidizing agent.
A reactant in a redox reaction that donates an electron to the
reduced species. The
reducing agent is oxidized.
The gain of an electron by a species (a decrease in oxidation number).
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.
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.
An arbitrarily defined set of conditions--273K, 1atm for gasses, or 1M for
Force over a distance.
Adding Cell Potentials
= Eo1 + Eo2
E = Eo - (RT/nF) ln Q