Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

2 CONSISTENCY WITH EQNS. OF TYPE -d[A]/dt = k[A]'[B]' 349if the values of k and k' were chosen correctly. For the purpose of elucidating thereaction mechanism, it is preferable to express the data by an equation of the secondtype rather than to constrain the data to the equation2.1 REACTIONS WITH KNOWN INVARIANT STOICHIOMETRYThe concentration-time data from a reaction whose stoichiometry has beenstudied independently of its rate and found to be invariant can be analysed muchmore rigorously than the data from a reaction whose stoichiometry is unknown.Every effort should be made to avoid this latter situation since the advantagesof a knowledge of the stoichiometry more than compensate for the time spent inobtaining the additional experimental observations which are required. Nowhereis this more obvious than when the stoichiometry is known and invariant so that thereaction can be writtenIt follows from the conditions of conservation thatandetc.and, therefore, if the concentration of A is known, the concentrations of the otherreactants and the products can be calculated from the volume of the system andtheir initial concentrations. The above equations simplify toPI = CBlo -(~Ea/V*~~CAIo - CAI) (7)Cp1 = [plO+(v~/vA)([AIO-~A1)etc.(8)for a reaction in which there is no change in volume as the reaction proceeds. Inthis case, the four alternative definitions of reaction rate are simply related to oneanother as can be seen by differentiating the above equations with respect to time.References p. 407