CHEM131 - Ch13 Electrochemistry

Active electrolysis

Electrolysis in which the electrode materials are reactants and products in the cell reaction.

Alkaline Battery

The most common single-use (primary) battery, so named because it uses a paste of KOH as the electrolyte.

Anode

Electrode at which oxidation takes place.

Battery

An electrochemical cell or series of cells in which a spontaneous redox reaction generates an electric current.

Cathode

Electrode at which reduction takes place.

Cathodic Protection

A method for preventing corrosion whereby the metal to be protected is connected electrically to a more reactive metal. The protected metal thus becomes the cathode, so it cannot be oxidized.

Cell Notation

Shorthand notation for an electrochemical cell that shows the electrodes, gases, and solutions in the cell reaction as well as the phase boundaries separating them.

Cell Potential

The electromotive force of an electrochemical cell. The amount of work the cell can do per coulomb of charge.

Corrosion

The degradation of metals exposed to the environment by chemical oxidation.

Crevice Corrosion

Corrosion in a small gap between two pieces of metal.

Electrochemistry

The study of the connection between oxidation-reduction reactions and the flow of electrons.

Electrodes

An electrically conducting site at which either oxidation or reduction takes place.

Electrolysis

Process in which an electric current is used to drive a redox reaction in its nonspontaneous direction.

Electromotive Force (EMF)

The difference in electric potential between the two electrodes in a galvanic cell. See also cell potential.

Eletroplating

The process of depositing a thin coat of metal on a surface by electrolysis.

Faraday Constant (F)

The electric charge on 1 mole of electrons; 96, 485 C mol^-1

Fuel Cell

An electrochemical cell in which reaction between a fuel and an oxidant produces electricity. Unlike a battery, a fuel cell uses a replenishable external supply of reactants.

Galvanic Cell

Any electrochemical cell in which a spontaneous chemical reaction generates an electric current. Also called a voltaic cell.

Galvanic Corrosion

Degradation of metal parts through oxidation that occurs only when two different metals are in contact with each other in the presence of an appropriate electrolyte.

Half-Reactions

A reaction showing only the oxidation or reduction process in a redox reaction.

Lead-Acid Storage Batteries

Secondary (rechargeable) battery used in the ignition system of automobiles, whose name derives from the use of lead in the electrodes and sulfuric acid as the electrolyte.

Lithium Batteries

A commercially available primary battery with a lithium anode and a manganese dioxide cathode. Used in calculators, watches, and medical devices.

Lithium-ion Batteries

A common secondary (rechargeable) battery in which lithium ions move from the anode to the cathode during use and in the opposite direction during recharging. Used in cell phones, laptop computers, and other portable electronic devices as well as some electric vehicles.

Nerst Equation

Mathematical equation relating the cell potential to the concentrations and pressures of chemical species in the cell reaction.

Nickel-Metal-Hydride Batteries

Secondary (rechargeable) battery used in many small electronic devices; involves the oxidation of hydrogen from a metal hydride and the reduction of nickel oxyhydroxide (NiO(OH)). Compared with older nicad batteries, NiMH eliminates the use of toxic cadmium and is less prone to memory effects.

Oxidation

The loss of electrons by some chemical species in a chemical reaction.

Oxidation-Reduction Reactions (Redox)

Chemical reaction involving the transfer of electrons from one species to another. Also called a redox reaction.

Passive Electrolysis

Electrolysis in which the electrodes are chemically inert materials that simply provide a pathway for electrons to enter and leave the electrolytic cell.

Primary Cell

A single-use battery that cannot be recharged.

Redox Reactions (Oxidation-Reduction Reactions).

A chemical reaction involving the transfer of electrons from one species to another. See also oxidation-reduction reaction.

Reduction

The gain of electrons by some chemical species in a chemical reaction.

Sacrificial Anode

A piece of a more reactive metal used to protect another metal from corrosion. The presence of the sacrificial anode assures that the part to be protected will be the cathode and hence will not be oxidized.

Salt Bridge

Device used to allow the flow of ions into the individual half-cell compartments in an electrochemical cell and maintain charge neutrality.

Secondary Cell

A battery that can be recharged by applying an external electric current to reverse the cell reaction and regenerate the reactants.

Standard Hydrogen Electrode (SHE)

Electrode used to define the scale of standard reduction potentials, consisting of a platinum electrode at which 1 M H3O+ ions are reduced to H2 gas at 1 atm.

Standard Reduction Potentials

The potential of an electrochemical cell consisting of the given half-reaction and a standard hydrogen electrode, measured with the SHE connected to the positive terminal of the voltmeter; provides a convenient measure of the tendency of a species to undergo oxidation or reduction.

Uniform Corrosion

Degradation of a metal surface by oxidation from uniform exposure to environmental moisture.

Zinc-Air Battery

A primary (non-rechargeable) cell in which zinc is oxidized at the anode and oxygen is reduced at the cathode. Because oxygen can be obtained on demand from the air, these batteries can have high energy density and are suitable for use as emergency power supplies for cell phones or other devices.