Chapter 7 - Chemical Equilibrium

Reaction Gibbs energy

The slope of the graph of the Gibbs energy plotted against the extent of the reaction

Exergonic

Since the process is spontaneous, it can be used to drive another process, such as another reaction, or used to do non-expansion work

Endergonic

The reaction can be made to occur only by doing work on it, such as electrolyzing water to reverse its spontaneous formation reaction

Standard reaction Gibbs energy

The difference in the standard molar Gibbs energies of the reactants and products

General case of a reaction

Thermodynamic equilibrium constant

An equilibrium constant K expressed in terms of activities

Le Chatelier's principle

A system at equilibrium, when subjected to a disturbance, responds in a way that tends to minimize the effect of the disturbance

Exothermic reactions

Increased temperature favors the reactants

Endothermic reactions

Increased temperature favors the products

Van 't Hoff equation

An expression for the slope of a plot of the equilibrium constant as a function of temperature.

Electrodes

Metallic conductors

Electrolyte

An ionic conductor

Salt bridge

A tube containing a concentrated electrolyte solution that completes the electrical circuit and enables the cell to function

Galvanic cell

An electrochemical cell that produces electricity as a result of the spontaneous reaction occurring inside it

Electrolytic cell

An electrochemical cell in which a non-spontaneous reaction is driven by an external source of current

Oxidation

The removal of electrons from a species

Reduction

The addition of electrons to a species

Redox reaction

Reaction in which there is a transfer of electrons from one species to another

Reducing agent (Reductant)

The electron donor

Oxidizing agent (Oxidant)

The electron acceptor

Redox couple

The reduced and oxidized species in a half-reaction

Anode

The electrode at which oxidation occurs

Cathode

The electrode at which reduction occurs

Electrolyte concentration cell

The electrode compartments are identical except for the concentrations of the electrolytes

Electrode concentration cell

When the electrodes themselves have different concentrations, either because they are gas electrodes operating at different pressures or because they are amalgams with different concentrations

Liquid junction potential

An additional source of potential difference across the interface of the two electrolytes

Cell reaction

The reaction in the cell written on the assumption that the right-hand electrode is the cathode

Cell potential

This potential difference

Electromotive force

The resulting potential difference

Nernst equation

Standard hydrogen electrode

The specially selected electrode

Standard potential

The right-hand electrode and the standard hydrogen electrode is the left-hand electrode

Electrochemical series

The metallic elements arranged in the order of their reducing power as measured by their standard potentials in an aqueous solution

Ion-selective electrode

An electrode that generates a potential in response to the presence of a solution of specific ions

Gas-sensing electrode

Consists of a glass electrode contained in an outer sleeve filled with an aqueous solution and separated from the test solution by a membrane that is permeable to gas

Asymmetry potential

Observed even when the activity of the test species is the same on both sides of the membrane