Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

2 CONSISTENCY WITH EQNS. OF TYPE -d[A]/dt = k[A]"[B]* 353T9 I I >b 0 lolog,Fig. 1. Variation of a with log,, 0 for simple orders.It should be noted that the displacement of the log,, (t - to) values from the log,, 8values is related to the rate coefficient k, the initial concentration [A],, and thestoichiometric ratio r by the expressionas can be seen from eqn. (17). Examination of the five curves of Fig. 1 shows thatit is not possible to discriminate between the five possible values of (a+b) if onlysmall extents of reactions are studied; for this reason, it is essential that the reactionbe followed until at least 60 or 70% of the reactants have been converted intoproducts. Although it is unlikely that there are any complications in the case ofreactions with an invariant stoichiemetry, it is desirable to c o b that the samecurve of a against log,, 0 fits the data obtained in a series of experiments at differentvalues of [A], and [B], subject to the condition that their ratio remains constantand equal to r. As a further check on the consistency of the data, a straightline of slope (a+b-1) should be obtained when the scale displacements areplotted against the logarithms of the initial concentrations of A.(ii) Alternative methods based on eqm. (15), (Z6), (17), (18) and (19)Fractional Zge method (I). It follows from either eqn. (18) or (19) that 8 is fixedfor a given value of a and (a+b). Therefore, if, in a series of experiments at differentvalues of the initial concentrations of A and B throughout which the ratisReferences p. 407