change of a quantity 

https://doi.org/10.1351/goldbook.C00968
The increment of the value of a quantity Q with time. The change may be expressed either infinitesimally at time t by the differential dQ or dQ(t), or in practice it may be expressed by a finite increment over the time interval (t1;t2), i.e. Q(t2)−Q(t1), which may be written ΔQ or ΔQ(t1;t2) ΔQ=ΔQ(t1;t2)=Q(t2)−Q(t1) Examples are: mass change, Δm; amount of substance change, Δn; volume change, ΔV; substance concentration change, Δc.
Source:
PAC, 1992, 64, 1569. (Quantities and units for metabolic processes as a function of time (IUPAC Recommendations 1992)) on page 1571 [Terms] [Paper]
Citation: 'change of a quantity' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C00968 RIS BibTex EndNote
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Last revised: February 24, 2014