Experimental kinetic data are most conveniently correlated by the integrated form of the differential rate equations which the reactions are presumed to obey. A new method of obtaining an approximate integral solution of the differential equations is described and applied to a set of three consecutive competitive reactions.The approximote integral solution is used to correlate experimental data on systems whose stoichiometry would indicate a consecutive competitive mechanism. The compositions of the reaction mixes are predicted with a standard error of estimate of less than 4% of the original concentration of the initiating reactant, in most cases less than 2%. The estimates of the rate constants, found by fitting the approximate solution to the data, are within experimental error of the values obtained by differentiation of the published results.Consider a set of irreversible consecutive reactions carried out at constant temperature k,
( 1 )The differential equations governing the course of the reaction set areatdt Because many addition, substitution, and polymerization reactions are stoichiometrically characterized by Equation ( 1 ) an integrated solution of Equations ( 2 ) is desirable. In the discussion to follow it will be assumed that only A and B are originalIy present and that the density of the system does not change as the reaction proceeds.To date the equations above have not been solved for the general case of any initial composition and any set of rate constants. In fact no solution has been reached for the simpler case in which only A and B are originally present. The equations have been solved for certain initial molar ratios and for particular sets of rate constants (7, 27), but these solutions can- (5,21,24,29,30) to determine the individual rate constants for consecutive competitive reaction systems. By suitable treatment of the differental equations Fuoss (8), Natta and Mantica (18), and others (1,4,11,15,22,23,25,26) have derived formulas which describe the distribution of converted A among the products as a function of the rate constants. Product distribution studies for similar but more complex reaction systems have also been reported (2, 3, 9). Thus, given the rate constants for the reaction set, if the quantity of A in the reaction mix could be computed, product distribution studies could then be used to predict the entire composition of the reaction mix at any time, for any set of initial conditions. Once this can be done, practical problems involving systems of consecutive cometitive reactions can be solved. It will Ee possible to correlate the large body of experimental data on systems whose stoichiometry obeys Equation (1) to see whether the mechanism of the reactions is well represented by the differential rate equations and to find rate constants for the twin purposes of extrapolation and design. Hence the first purpose of this paper is the development of equations describing the time dependence of the concentration of A.
M. H. Friedman is with the Minnesota
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