Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

2 CONSISTENCY WITH EQNS. OF TYPE -d[A]/dt = k[A]"[B]* 391A more important consideration is the choice of z. If we choose a very largevalue of z, we have the same problem as discussed under Guggenheim's method,namely that our slope is determined by the very early and very late values of 4, theintermediate values being unused; we also unnecessarily inflate the standard errorof the slope by having too few points define the straight line. If we choose a verysmall value of z, we run into a somewhat different problem to that whicharises withthe Guggenheim method. In the Mangelsdorf method, the magnitude of theobserved slope depends on the value of z selected-the smaller the value of z,the smaller the slope. The implications can be seen by writing the slope of theMangelsdorf plot as S and considering the relation of its standard error to thestandard error of the rate coefficient. We writeand therefore1a(k) = - a(S)SzThereforeThus if kz