  For some centuries, first order chemical rate constants were determined
mainly by a linear logarithmic plot of reagent concentration terms against time
where the initial concentration was required, which is experimentally often a
challenging task to derive accurate estimates. By definition, the rate constant
was deemed to be invariant and the kinetic equations were developed with this
assumption. A reason for these developments was the ease in which linear graphs
could be plotted. Here, different methods are discussed that does not require
exact knowledge of initial concentrations and which require elementary
nonlinear analysis and the ensuing results are compared with those derived from
the standard methodology from an actual chemical reaction, with its
experimental determination of the initial concentration with a degree of
uncertain. We verify experimentally our previous theoretical conclusion based
on simulation data [ J. Math . Chem {\bf 43} (2008) 976--1023,
arXiv:physics/0608073] that the so called rate constant is never constant even
for elementary reactions and that all the rate laws and experimental
determinations to date are actually averaged quantities over the reaction
pathway. We conclude that nonlinear methods in conjunction with experiments
could in the future play a crucial role in extracting information of various
kinetic parameters.
