Examples of combinations of processes in reaction mechanisms giving nonlinear differential equations and other integrated expressions will be seen later. Nonlinear time differentials result from the combination of linear time differentials and give rise to other snapshot equations. There are sets of limiting or model conditions which define ideal chemical reactors. These model conditions may be approached in practice by real experimental reactors, although some real reactors are intermediate between the limiting models. Ideal reactors have characteristics which can be described mathematically in a far simple fashion than real, non-ideal reactors.
Many industrial processes use flow systems, while batch reactors are most common in the laboratory.
Any steady state situation is preceded by an initial transient condition, although this may be immeasurably fast as far as our method of detection is concerned. If you watch ants moving around, you notice that as the temperature increases the rate of activity increases. Measured carefully, the activity doubles about every ten degrees celsius, reflecting some fundamental metabolic chemical process that has this temperature dependence. You can check this mathematically or graphically. The relaxation time is the reciprocal of the rate coefficient for a simple unimolecular process.