Names of quantities

A substanceis a distinct, pure form of matter. The amount of substance, n (more colloquially ‘number of moles’ or ‘chemical amount’), in a sample is reported in terms of the mole(mol): 1 mol is the amount of substance that contains as many objects (atoms, molecules, ions, or other specified entities) as there are atoms in exactly 12g of carbon-12. This number is found experimentally to be approximately 6.02 ×1023 (see the endpapers for more precise values). If a sample contains N entities, the amount of substance it contains is n=N/NA, where NA is the Avogadro constant: NA=6.02× 1023mol−1. Note that NA is a quantity with units, not a pure number. An extensive property is a property that depends on the amount of substance in the sample. Two examples are mass and volume. An intensive property is a property that is independent of the amount of substance in the sample. Examples are temperature, mass density (mass divided by volume), and pressure. A molar property , Xm, is the value of an extensive property, X, of the sample divided by the amount of substance present in the sample: Xm=X/n. A molar property is intensive. An example is the molar volume ,Vm, the volume of a sample divided by the amount of substance in the sample (the volume per mole). The one exception to the notation Xm  is the molar mass, which is denoted M. The molar mass of an element is the mass per mole of its atoms. The molar mass of a molecular compound is the mass per mole of molecules, and the molar mass of an ionic compound is the mass per mole of formula units. A formula unit of an ionic compound is an assembly of ions corresponding to the chemical formula of the compound; so the formula unit NaCl consists of one Na+ ion and one Cl− ion. The names atomic weight and molecular weight are still widely used in place of molar mass (often with the units omitted), but we shall not use them in this text. The molar concentration (‘molarity’) of a solute in a solution is the amount of substance of the solute divided by the volume of the solution. Molar concentration is usually expressed in moles perdecimetre cubed (mol dm⁻³ or mol L−1; 1 dm³ is identical to 1 L). A solution in which the molar concentration of the solute is 1 mol dm−3 is prepared by dissolving 1 mol of the solute in sufficient solvent to prepare 1 dm³ of solution. Such a solution is widely called a ‘1 molar’ solution and denoted 1 m. The term molality refers to the amount of substance of solute divided by the mass of solvent used to prepare the solution. Its units are typically moles of solute per kilogram of solvent (mol kg⁻¹).

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Units

Working galvanic cells

Electrolysis

Experimental techniques

The rate laws

The electric potential at the interface

The structure of the interface

Catalytic activity at surfaces

Mechanisms of heterogeneous catalysis

Mobility on surfaces

The rate of desorption

The rate of adsorption