rate of formation, νn,y, νc,y

https://doi.org/10.1351/goldbook.R05152
Like the
rate of consumption
, the rate of formation of a specified product may be defined in two ways:
  1. As the time derivative of the amount of a product. Thus for a product Y, present at any time in amount nY. the rate of its formation may be given by: ν(nY)=dnYdt This definition is particularly appropriate for open systems.
  2. For kinetics in closed systems it is more usual to define a rate of formation per unit volume, denoted ν(cY): ν(cY)=1VdnYdt When the volume is constant this reduces to: ν(cY)=1VdnYdt=d[Y]dt When the volume is not constant the relationship nY=[Y]V may be differentiated to give: dnY=Vd[Y]+[Y]dV and the rate of formation becomes: ν(cY)=d[Y]dt+[Y]VdVdt A rate of formation may be specified even for a reaction of time dependent
    stoichiometry
    or of unknown
    stoichiometry
    .
Source:
PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 181 [Terms] [Paper]