CHAP. 1: BASIC TERMS [CONTENTS] 34
1.5 Some basic and derived quantities
1.5.1 Massm
U Main unit:kg.
1.5.2 Amount of substancen.
U Main unit:mol. 1 mol isNAof particles (atoms, molecules, ions... ), whereNA= 6. 022025 × 1023
is theAvogadro constant.
1.5.3 Molar massM
U Main unit: kg mol−^1. The molar mass is the mass of one mole of particles. The relation between
the amount of substance, mass and molar mass is
n=m/M. (1.3)
This relation applies to both a pure substance and a mixture. The molar mass of a mixture
can be calculated using the relationM=
∑ki=1xiMi, (1.4)whereMiis the molar mass of componenti, andxiis its mole fraction [see1.6.1]1.5.4 Absolute temperatureT
U Main unit:K.
Note:Temperature given in◦C is denotedt(t= T – 273.15)1.5.5 Pressurep
U Main unit:Pa.
Older units:bar (1 bar = 10^5 Pa), atm (1 atm = 101 325 Pa), torr (760 torr = 101 325 Pa).