Accuracy of enthalpy and entropy determination using the kinetic method: Are we approaching a consensus?

L. Drahos, Csaba Peltz, K. Vékey

Research output: Contribution to journalArticle

56 Citations (Scopus)

Abstract

There is an emerging consensus regarding the applicability of the kinetic method. All parties acknowledge that it is an approximate quantitative technique, capable of yielding not only enthalpy, but also entropy values. Opinions differ mainly on the accuracy of the results but it is agreed that the energy (effective temperature) dependence of kinetic method plots needs to be checked in all but the simplest of cases. When the 'apparent basicity' is found to depend on collision energy (and hence effective temperature), the extended kinetic method must be used. We have performed a large-scale modeling study, involving thousands of randomly selected molecular systems and a variety of experimental conditions, using exact calculations and realistic data sets. The results show that when the measured entropy difference between the two competing reaction channels is less than ∼35 J mol-1 K-1, overall errors (standard deviations) of ΔH298 determined by the kinetic method are ±5 kJ mol-1; those of ΔS298 are ±10 J mol-1 K-1. These include not only inherent errors of the kinetic method, but also errors in ion abundance measurement (5%) and inaccurate knowledge of reference compound thermochemistry (±2 kJ mol-1, on average). We recommend, in general, that these errors be reported in kinetic method studies. When the measured entropy difference between the two competing fragmentation channels is large (>35 J mol-1 K-1), it is likely to be significantly underestimated and errors of the kinetic method increase significantly.

Original languageEnglish
Pages (from-to)1016-1024
Number of pages9
JournalJournal of Mass Spectrometry
Volume39
Issue number9
DOIs
Publication statusPublished - Sep 2004

Fingerprint

Entropy
Enthalpy
enthalpy
entropy
Kinetics
kinetics
Thermochemistry
Temperature
thermochemistry
Alkalinity
standard deviation
emerging
fragmentation
plots
Ions
temperature dependence
collisions
energy
ions

Keywords

  • Collision-induced dissociation
  • Entropy
  • Kinetic method
  • Mass spectrometry
  • RRKM

ASJC Scopus subject areas

  • Organic Chemistry
  • Spectroscopy
  • Biophysics

Cite this

Accuracy of enthalpy and entropy determination using the kinetic method : Are we approaching a consensus? / Drahos, L.; Peltz, Csaba; Vékey, K.

In: Journal of Mass Spectrometry, Vol. 39, No. 9, 09.2004, p. 1016-1024.

Research output: Contribution to journalArticle

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