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INTERNATIONAL ISO
STANDARD 80000-9
Second edition
2019-08
Quantities and units —
Part 9:
Physical chemistry and molecular
physics
Grandeurs et unités —
Partie 9: Chimie physique et physique moléculaire
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
Bibliography .15
Index .16
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www. iso. org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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on the ISO list of patent declarations received (see www. iso.o rg/patents).
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.org/iso/foreword. html.
This document was prepared by Technical Committee ISO/TC 12, Quantities and units, in collaboration
with Technical Committee IEC/TC 25, Quantities and units.
This second edition cancels and replaces the first edition (ISO 80000-9:2009), which has been
technically revised. It also incorporates the Amendment ISO 80000-9:2009/Amd. 1:2011.
The main changes compared to the previous edition are as follows:
— the table giving the quantities and units has been simplified;
— some definitions and the remarks have been stated physically more precisely.
A list of all parts in the ISO 80000 and IEC 80000 series can be found on the ISO and IEC websites.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www. iso. org/members. html.
iv © ISO 2019 – All rights reserved
Introduction
In this document, symbols for substances are shown as subscripts, for example c , w , p for substance B.
B B B
Generally, it is advisable to put symbols for substances and their states in parentheses on the same line
as the main symbol, for example c(H SO ).
2 4
In the following, the letter s is used to denote the solid state, the letter l the liquid state, and the letter g
the gaseous state.
The symbol * used as a superscript means “pure”.
⊝
The plimsoll sign is used to denote a standard in general.
∗
EXAMPLE 1 μ (,Tp) for chemical potential of pure substance B concerning a mixture system including the
B
substance B.
−−11
EXAMPLE 2 C (H O,g,298,15K)=⋅33,58 JK ⋅mol for standard molar heat capacity at constant
m,p 2
pressure.
In an expression such as
V
m,B
ϕ =x
BB
xV
∑ i m,i
where
ϕ is the volume fraction of a particular substance B in a mixture of substances A, B, C, …;
B
x is the amount-of-substance fraction of i; and
i
V is the molar volume of the pure substance i, where all the molar volumes V , V ,V , .
m,i m,A m,B m,C
are taken at the same temperature and pressure,
the summation on the right-hand side is that over all the substances A, B, C, . of which a mixture is
composed, so that x =1 . Throughout the document sums are running over the respective index.
∑ i
Additional qualifying information on a quantity symbol may be added as a subscript or superscript (see
e.g. item 9-21) or in parentheses after the symbol.
INTERNATIONAL STANDARD ISO 80000-9:2019(E)
Quantities and units —
Part 9:
Physical chemistry and molecular physics
1 Scope
This document gives names, symbols, definitions and units for quantities of physical chemistry and
molecular physics. Where appropriate, conversion factors are also given.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
Names, symbols, definitions and units for quantities used in physical chemistry and molecular physics
are given in Table 1.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
2 © ISO 2019 – All rights reserved
Table 1 — Quantities and units used in physical chemistry and molecular physics
Item No. Quantity Unit Remarks
Name Symbol Definition
9-1 number of entities number of elementary entities of kind X in a system 1 The elementary entities must be specified
N()X ,
and can be atoms, molecules, ions, elec-
N trons, other particle, or a specified group
X
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 mate-
rial involved.
9-2 amount of substance quotient of number N of specified elementary mol Amount of substance is one of the seven
n()X
entities of kind X (item 9-1) in a sample, and the base quantities in the International System
DEPRECATED: num-
of Quantities, ISQ (see ISO 80000-1).
Avogadro constant N (ISO 80000-1):
ber of moles
A
Elementary entities, such as molecules,
nN()XX= ()/N
A
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 H , 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, HCl”, or
“amount of benzene, C H ”.
6 6
The name “number of moles” is often used
for “amount of substance”, but this is depre-
cated because the name of a quantity should
be distinguished from the name of the unit.
Table 1 (continued)
Item No. Quantity Unit Remarks
Name Symbol Definition
9-3 relative atomic mass quotient of the average mass (ISO 80000-4) of atom 1 A similar quantity “relative molecular
A ()X
r
X and the unified atomic mass (ISO 80000-10) mass” can be defined for molecules.
EXAMPLE
A ()Cl ≈35,453,
r
A CO ≈44.
()
r 2
The relative atomic or relative molecular
mass depends on the nuclidic composition.
The International Union of Pure and Applied
Chemistry (IUPAC) accepts the use of the
special names “atomic weight” and “mo-
lecular weight” for the quantities “relative
atomic mass” and “relative molecular mass”,
respectively. The use of these traditional
names is deprecated.
9-4 molar mass for a pure substance X, quotient of mass m(X) g/mol
M X
()
(ISO 80000-4) and amount n of substance (item
−1
kg mol
9-2):
Mm= /n
3 −1
9-5 molar volume V for a pure substance, quotient of its volume V m mol
m
(ISO 80000−3) and amount n of substance (item
9-2):
VV= /n
m
9-6.1 molar internal U quotient of internal energy U (ISO 80000-5) and J/mol Molar quantities are normally only used with
m
energy amount n of substance (item 9-2): reference to pure substances.
2 −2 −1
kg m s mol
UU= /n
m
9-6.2 molar enthalpy H quotient of enthalpy H (ISO 80000-5) and amount J/mol Molar quantities are normally only used with
m
n of substance (item 9-2): reference to pure substances.
2 −2 −1
kg m s mol
HH= /n
m
4 © ISO 2019 – All rights reserved
Table 1 (continued)
Item No. Quantity Unit Remarks
Name Symbol Definition
9-6.3 molar Helmholtz F quotient of the Helmholtz energy F (ISO 80000-5) J/mol Molar quantities are normally only used with
m
energy and amount n of substance (item 9-2): reference to pure substances.
2 −2 −1
kg m s mol
FF= /n
m
9-6.4 molar Gibbs energy G quotient of the Gibbs energy G (ISO 80000-5) and J/mol Molar quantities are normally only used with
m
amount n of substance (item 9-2): reference to pure substances.
2 −2 −1
kg m s mol
GG= /n
m
9-7 molar heat capacity C quotient of heat capacity C (ISO 80000-5) and J/(mol K) Conditions (constant pressure or volume etc.)
m
amount of substance n (item 9-2): must be specified.
2 −2 −1 −1
kg m s K mol
CC= /n
m
9-8 molar entropy S quotient of entropy S (ISO 80000-5) and amount n J/(mol K) Conditions (constant pressure or volume etc.)
m
of substance (item 9-2): must be specified.
2 −2 −1 −1
kg m s K mol
SS= /n
m
–3
9-9.1 particle n, (C) quotient of number N of particles (item 9-1) and m The term “number density” is also used.
concentration volume V (ISO 80000−3):
nN= /V
–3
9-9.2 molecular concen- C(X), C for substance X in a mixture, quotient of num- m
X
tration ber N of molecules of substance X and volume V
X
(ISO 80000−3) of the mixture:
CN= /V
XX
th
9-10 mass concentration γ , (ρ ) for substance X in a mixture, quotient of mass g/l Decided by the 16 CGPM (1979), both “l” and
X X
m (ISO 80000-4) of substance X and volume V “L” are allowed for the symbols for the litre.
X −3
kg m
(ISO 80000−3) of the mixture:
γ =mV/
XX
9-11 mass fraction w for substance X in a mixture, quotient of mass m 1
X X
(ISO 80000-4) of substance X and total mass m of
the mixture:
wm= /m
XX
Table 1 (continued)
Item No. Quantity Unit Remarks
Name Symbol Definition
9-12.1 amount-of-substance c for substance X in a mixture, quotient of amount mol/l In chemistry, the name “amount-of-substance
X
concentration n of substance (item 9-2) of X and volume V concentration” is generally abbreviated to the
X –3
mol m
(ISO 80000−3) of the mixture: single word “concentration”, it being assumed
that the adjective “amount-of-substance” is
cn= /V
intended. For this reason, however, the word
XX
“mass” should never be omitted from the name
“mass concentration” in item 9-10.
th
Decided by the 16 CGPM (1979), both “l” and
“L” are allowed for the symbols for the litre.
th
9-12.2 standard amount-of- for substance X, one mole per litre mol/l Decided by the 16 CGPM (1979), both “l” and
c X
()
substance “L” are allowed for the symbols for the litre.
−3
mol m
concentration
9-13 amount-of-substance x , y for substance X in a mixture, quotient of amount of 1 For condensed phases, x is used, and for
X X X
fraction substance n (item 9-2) of X and total amount n of gaseous mixtures y may be used.
X X
substance (item 9-2) in the mixture:
mole fraction The unsystematic name “mole fraction” is
still used. However, the use of this name is
xn= /n
XX
deprecated.
For this quantity, the entity used to define
the amount of substance should always be
a single molecule for every species in the
mixture.
9-14 volume fraction for substance X, quotient of product of amount of ml/l Generally, the volume fraction is temperature
ϕ
X
substance fraction x (item 9-13) of X and molar dependent.
X
volume V (item 9-5) of the pure substance X at
m,X th
Decided by the 16 CGPM (1979), both “
...