Amount of substance

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Amount of substance

Description

The amount of substance, n, is a base physical quantity, and the corresponding SI unit is the mole [mol]. Amount of substance (sometimes abbreviated as 'amount' or 'chemical amount') is proportional to the number of specified elementary entities, N_i of that substance i, and the universal proportionality constant is the reciprocal value of the Avogadro constant [1],

ni = Ni/NA

n_i contained in a system can change due to internal and external transformations,

dni = dini + deni

In the absence of nuclear reactions, the amount of any atom is conserved, e.g., for carbon d_in_C = 0. This is different for chemical substances or ionic species which are produced or consumed during the advancement of a reaction, r,

A change in the amount of i, dn_i, in an open system is due to both the internal formation in chemical transformations, d_rn_i, and the external transfer, d_en_i, across the system boundaries. dn_i is positive if i is formed as a product of the reaction within the system. d_en_i is negative if i flows out of the system and appears as a product in the surroundings [2].

Abbreviation: n [mol]

Reference: Cohen 2008 IUPAC Green Book, Gnaiger 1993 Pure Appl Chem

Communicated by Gnaiger E (last update 2018-11-02)

Quantity	Symbol for quantity Q	Symbol for dimension	Name of abstract unit uQ	Symbol for unit uQ [*]
elementary entity *,$	UX	U	elementary unit	x
count *,$	NX = N·UX	X	elementary unit	x
amount of substance *,§	nX = NX·NA-1	N	mole	mol
charge *,€	Qel = zX·e·NX	I·T	coulomb	C = A·s
length	l	L	meter	m
mass	m	M	kilogram	kg
time	t	T	second	s
electric current	I	I	ampere	A
thermodynamic temperature	T	Θ	kelvin	K
luminous intensity	Iv	J	candela	cd

[*] SI units, except for the canonical 'elementary unit' [x]. The following footnotes are canonical comments, related to iconic symbols.

^* For the elementary quantities N_X, n_X, and Q_el, the entity-type X of the elementary entity U_X has to be specified in the text and indicated by a subscript: n_O2; N_ce; Q_el.

^$ Count N_X equals the number of elementary entities U_X. In the SI, the quantity 'count' is explicitly considered as an exception: "Each of the seven base quantities used in the SI is regarded as having its own dimension. .. All other quantities, with the exception of counts, are derived quantities" (Bureau International des Poids et Mesures 2019 The International System of Units (SI)). An elementary entity U_X is a material unit, it is not a count (U_X is not a number of U_X). N_X has the dimension X of a count and U_X has the dimension U of an elementary entity; both quantities have the same abstract unit, the 'elementary unit' [x].

^§ Amount n_X is an elementary quantity, converting the elementary unit [x] into the SI base unit mole [mol] using the Avogadro constant N_A.

^€ Charge is a derived SI quantity. Charge is an elementary quantity, converting the elementary unit [x] into coulombs [C] using the elementary charge e, or converting moles [mol] into coulombs [C] using the Faraday constant F. z_X is the charge number per elementary entity U_X, which is a constant for any defined elementary entity U_X. Q_el = z_X·F·n_X

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Entity, count, and number, and SI base quantities / SI base units

Quantity name	Symbol	Unit name	Symbol	Comment
elementary	UX	elementary unit	[x]	UX, UB; [x] not in SI
count	NX	elementary unit	[x]	NX, NB; [x] not in SI
number	N	-	dimensionless	= NX·UX-1
amount of substance	nB	mole	[mol]	nX, nB
electric current	I	ampere	[A]	A = C·s-1
time	t	second	[s]
length	l	meter	[m]	SI: metre
mass	m	kilogram	[kg]
thermodynamic temperature	T	kelvin	[K]
luminous intensity	IV	candela	[cd]

Fundamental relationships

» Avogadro constant N_A

» Boltzmann constant k

» elementary charge e

» Faraday constant F

» gas constant R

» electrochemical constant f

SI and related concepts

» International System of Units

» elementary unit x

» SI prefixes

» International Union of Pure and Applied Chemistry, IUPAC

» entity

» quantity

» dimension

» format

» motive unit

» iconic symbols

References

1. Bureau International des Poids et Mesures (2019) The International System of Units (SI). 9th edition:117-216 ISBN 978-92-822-2272-0. - »Open Access pdf«
2. Cohen ER, Cvitas T, Frey JG, Holmström B, Kuchitsu K, Marquardt R, Mills I, Pavese F, Quack M, Stohner J, Strauss HL, Takami M, Thor HL (2008) Quantities, Units and Symbols in Physical Chemistry. IUPAC Green Book 3rd Edition, 2nd Printing, IUPAC & RSC Publishing, Cambridge. - »Bioblast link«
3. Gnaiger E (1993) Nonequilibrium thermodynamics of energy transformations. Pure Appl Chem 65:1983-2002. - »Bioblast link«

1. Gnaiger E (2019) Mitochondrial pathways and respiratory control. An introduction to OXPHOS analysis. 5th ed. Mitochondr Physiol Network 24.05. Oroboros MiPNet Publications, Innsbruck:112 pp. - »Bioblast link«

MitoPedia concepts: MiP concept, Ergodynamics 

MitoPedia topics: Substrate and metabolite