Like the rate of consumption
the rate of formation of a specified product may be defined in two ways:
As the time derivative of the amount of a product. Thus for a product Y, present at any time in amount
the rate of its formation may be given by:
This definition is particularly appropriate for open systems.
For kinetics in closed systems it is more usual to define a rate of formation per unit volume, denoted
When the volume is constant this reduces to:
When the volume is not constant the relationship
may be differentiated to give:
and the rate of formation becomes:
A rate of formation may be specified even for a reaction of time dependent stoichiometry or of unknown stoichiometry.
PAC, 1996, 68, 149
(A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996))
on page 181
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. doi:10.1351/goldbook