Double Exponential Evaluation under Non-Pseudo–First-Order Conditions: A Mixed Second-Order Process Followed by a First-Order Reaction

Virág Kiss, K. Ősz

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4 Citations (Scopus)

Abstract

In this paper, a double exponential approximating approach is described for a quite common kinetic model (mixed second-order formation of an intermediate followed by its first-order decay) under non-pseudo–first-order conditions (i.e., when the initial ratio of the two reactants is between 1 and 10). For the evaluation, first the exact kinetic curves predicted by the two-step model were calculated and then fitted to a double exponential function. The goodness of the fits and the estimated parameters of the double exponential function for both I and P concentrations were determined as a function of the rate constants and initial concentrations in the two-step model. It was found that the fit of the double exponential function is acceptable or very good under these conditions despite the fact that none of the reagents is in a large excess. Since UV–vis absorption spectroscopy is probably the most common technique to follow kinetic traces, we also made efforts to deal with the typical properties of monitoring the process through UV–vis. It was found that the experimental curves can be fitted quite well with a double exponential function if the reagents have minor absorption compared to the intermediate and/or product. The connection between the observed rate constants and the rate constants of the above-mentioned mechanism is also studied.

Original languageEnglish
Pages (from-to)602-610
Number of pages9
JournalInternational Journal of Chemical Kinetics
Volume49
Issue number8
DOIs
Publication statusPublished - Aug 1 2017

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Exponential functions
exponential functions
Rate constants
evaluation
Kinetics
reagents
kinetics
Spectrum Analysis
curves
Absorption spectroscopy
absorption spectroscopy
Monitoring
decay
products

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

Cite this

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AB - In this paper, a double exponential approximating approach is described for a quite common kinetic model (mixed second-order formation of an intermediate followed by its first-order decay) under non-pseudo–first-order conditions (i.e., when the initial ratio of the two reactants is between 1 and 10). For the evaluation, first the exact kinetic curves predicted by the two-step model were calculated and then fitted to a double exponential function. The goodness of the fits and the estimated parameters of the double exponential function for both I and P concentrations were determined as a function of the rate constants and initial concentrations in the two-step model. It was found that the fit of the double exponential function is acceptable or very good under these conditions despite the fact that none of the reagents is in a large excess. Since UV–vis absorption spectroscopy is probably the most common technique to follow kinetic traces, we also made efforts to deal with the typical properties of monitoring the process through UV–vis. It was found that the experimental curves can be fitted quite well with a double exponential function if the reagents have minor absorption compared to the intermediate and/or product. The connection between the observed rate constants and the rate constants of the above-mentioned mechanism is also studied.

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