The goal of reaction kinetics is to derive and parameterise a mathematical expression for the rate of change of a species in a reacting environment. Once a rate law \[ \dot r = \frac{\partial [{\rm A}]}{\partial t} = f(T,[\dots]) \] is estabished, the evolution of the reacting system—and hence the change in concentrations with time—can be calculated.
The rate of an elementary reaction \[ n{\rm A} + m{\rm B} + \dots \rightarrow k[{\rm C}] + l[{\rm D}] + \dots \] can be written as \[ \dot r = \frac{\partial_t [{\rm A}]}{n} = \frac{\partial_t [{\rm B}]}{m} = \frac{\partial_t [{\rm C}]}{k} = \frac{\partial_t [{\rm D}]}{l} = k\cdot [{\rm A}]^\alpha [{\rm B}]^\beta… \]
Elementary reactions
A number of achetypical elementary reactions are easily defined.
| name | reaction | rate law |
|---|---|---|
| first order | ||
| second order | ||
The stoichiometric factor is reflected in the rate law for an elementary reaction, which can be written as: \[ n{\rm A} + m{\rm B} + … \xrightarrow{\rm elementary} {\rm products} \quad\therefore\quad \dot r = [{\rm A}]^n[{\rm B}]^m… \]