Mole (unit) measure the amount of substance (although in practice it is usual). There are many physical relationships between amount of substance and other physical quantities, the most notable one being the ideal gas law (where the relationship was first demonstrated in 1857). The term "mole" was first used in a textbook describing these colligative properties. Chemical engineers use the unit extensively, and decimal multiples may be more suitable for industrial use. For convenience in avoiding conversions in the imperial (or American customary units), some engineers adopted the "pound-mole" (notation "lb-mol" or "lbmol"), which is defined as the number of entities in
Gas constant "V" is the volume of gas (SI unit cubic metres), "n" is the amount of gas (SI unit moles), "m" is the mass (SI unit kilograms) contained in "V", and "T" is the thermodynamic temperature (SI unit kelvins). "R" is the molar-weight-specific gas constant, discussed below. The gas constant is expressed in the same physical units as molar entropy and molar heat capacity. From the general equation "PV" = "nRT" we get: where "P" is pressure, "V" is volume, "n" is number of moles of a given substance, and "T" is temperature. As pressure is defined as force per unit