Chapter 18

Vocabulary flashcards related to electrochemistry concepts such as redox reactions, oxidation states, electrochemical cells, and cell potentials.

Redox Reaction

A reaction where one or more elements change oxidation number; always involves both oxidation and reduction.

Oxidizing Agent

The reactant molecule that causes oxidation and contains the element reduced.

Oxidation

The process that occurs when the oxidation number of an element increases, the element loses electrons, a compound adds oxygen, or a compound loses hydrogen.

Reduction

The process that occurs when the oxidation number of an element decreases, the element gains electrons, a compound loses oxygen, or a compound gains hydrogen.

Free Element Oxidation State

The oxidation state of a free element is always 0.

Monatomic Ion Oxidation State

The oxidation state of a monatomic ion is equal to its charge.

Sum of Oxidation States in a Compound

The sum of the oxidation states of all the atoms in a compound is 0.

Sum of Oxidation States in a Polyatomic Ion

The sum of the oxidation states of all the atoms in a polyatomic ion equals the charge on the ion.

Group I Metal Oxidation State

Group I metals have an oxidation state of +1 in all their compounds.

Group II Metal Oxidation State

Group II metals have an oxidation state of +2 in all their compounds.

Reducing Agent

The reactant that reduces an element in another reactant; it contains the element that is oxidized.

Electrical Current

The amount of electric charge that passes a point in a given period of time.

Electrochemistry

The study of redox reactions that produce or require an electric current.

Electrochemical Cell

A cell in which the conversion between chemical energy and electrical energy is carried out.

Voltaic Cell

A cell where spontaneous redox reactions take place (also known as galvanic cells).

Electrolytic Cell

A cell where nonspontaneous redox reactions can be made to occur by the addition of electrical energy.

Half-Cells

Separate oxidation and reduction reactions.

Electrode

A conductive solid (metal or graphite) that allows the transfer of electrons in an electrochemical cell.

Anode

The electrode where oxidation occurs; anions are attracted to it.

Cathode

The electrode where reduction occurs; cations are attracted to it.

Salt Bridge

Required to complete the circuit and maintain charge balance in a voltaic cell.

Current (Ampere)

The number of electrons that flow through the system per second; 1 A = 1 Coulomb of charge flowing by each second.

Potential Difference (Volt)

The difference in potential energy between the reactants and products; 1 V = 1 J of energy/Coulomb of charge.

Electromotive Force (emf)

The amount of force pushing the electrons through the wire.

Cell Potential

The difference in potential energy between the anode and the cathode in a voltaic cell.

Standard EMF (E°cell)

The cell potential under standard conditions (25°C, 1 atm for gases, 1 M concentration of solution).

Cell Notation

A shorthand description of a voltaic cell: electrode | electrolyte || electrolyte | electrode.

Standard Hydrogen Electrode (SHE)

The standard half-reaction for measuring half-cell potentials, defined as the reduction of H+ to H2 under standard conditions, with a potential difference = 0 V.

Nernst Equation

E = E° - (0.0592/n) log Q at 25°C, used to calculate E when concentrations are not 1 M.

Gibbs Free Energy and Cell Potential

ΔG° = -nFE°cell, relates the change in Gibbs free energy to the cell potential.