only apparent, of the reaction: see Section 4.4. Also the rate constant is an
empirical quantity to be experimentally determined, and it depends on the
reaction order. The combined knowledge of the order, the rate constant, and
the initial concentration of the reactant(s) allows calculation of changes
occurring. An example is prediction of the extent to which a certain
component is formed or degraded during long storage of a food. As is
illustrated in Figure 4.2, it may need very precise determination of the time
dependent concentration of a reaction product to establish the order, as long
as the reaction has not proceeded very far.
Another difference among the rates of reactions of various order is, of
course, the dependence on the concentration of the reactant(s). As seen in
Table 4.1, the rate is independent of concentration for zero-order,
proportional to concentration for first-order, and proportional to concen-
tration squared for second-order reactions.
FIGURE4.2 The change in concentration of reactant A with time for reactions of
order 0, 1, and 2.kis the rate constant;tis time.