BS EN ISO 80000-9:2019 pdf free.Quantities and units.
The elementary entities must be specified and can be atoms, molecules, ions, electrons, other particle, or a specified group of such particles. It is important to always give a precise specification of the entity involved; this should preferably be done by the empirical chemical formula of the material involved. Amount of substance is one of the seven base quantities in the International System of Quantities, ISQ (see ISO 80000-1). Elementary entities, such as molecules, atoms, ions, electrons, holes and other quasi-particles, double bonds can be used. It is necessary to specify precisely the entity involved, e.g. atoms of hydrogen H vs. molecules of hydrogen H2, preferably by giving the molecular chemical formula of the material involved.
In the name “amount of substance”, the words “of substance” could be replaced by words specifying the substance concerned, e.g. “amount of hydrogen chloride, HCI”, or “amount of benzene, C6H6”. The name “number of moles” is often used for “amount of substance”, but this is deprecated because the name of a quantity should be distinguished from the name of the unit.The alternative symbol mB should be avoided in situations where it might be mistaken for the mass of substance B. However, the symbol mB is much more commonly used than the symbol bB for molality, despite the possible confusion with mass. Mostly, molar or specific quantity is used and phase transition is expressed explicitly, e.g. molar latent heat of evaporation.
The subscript “pt” is the qualifier for the phase transition, which may be changed to e.g. “1-g”. The term “enthalpy of phase transition” is mainly used in theory. For a pure substance, where Gm is the molar Gibbs energy. In a mixture, p is the partial molar Gibbs energy. In condensed matter physics, the chemical potential of electrons is energy.BS EN ISO 80000-9 pdf download.