Chemically reacting mixtures

Stoichiometry

We denote the mass of a constituent

α

in a homogeneous mixture by

m

α

. The corresponding mass balance reads

$ {{{\rm d}m_\alpha} \over {{\rm d}t}} = \tau_{\alpha}V, \alpha = 1,2, \cdots, v, $

(9.1)

where

τ

α

is the density of mass production of constituent

α

. It is clear that the sum of all the

v

values

τ

α

must be equal to zero, because the total mass is conserved in a chemical reaction. However, this is not the only condition which the production densities

τ

α

must satisfy. Further conditions follow from the fact that the number of atoms – and their masses – must be conserved in the reaction; the atoms present before the reaction are still present after the reaction, although they may have changed their arrangement in molecules. The investigations of the conditions for this kind of arrangement is the subject of stoichiometry (Greek: stoichos “order” and metron “measure”).