The time derivative
of the value of the quantity. The differential quotient may also be called derivative
(or instantaneous) rate of change. Examples are: rate of change of mass,
;
rate of change of amount of substance,
.

Source:

PAC, 1992, *64*, 1569*
(Quantities and units for metabolic processes as a function of time (IUPAC Recommendations
1992))
* on page 1572