The increment of the value of a quantity

with time.
The change may be expressed either infinitesimally at time

by the differential

or

,
or in practice it may be expressed by a finite increment over the
time interval
, i.e.

, which may be written

or

Examples are: mass change,

;
amount of substance change,

; volume change,

;
substance concentration change,
.Source:
PAC, 1992, 64, 1569
(Quantities and units for metabolic processes as a function of time (IUPAC Recommendations
1992))
on page 1571
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.