Derivation of thermodynamic quantities from kinetic measurements

Results are presented of both traditional equilibrium and also gas phase kinetic measurements. These results are used to show, — (1) that measured enthalpies of formation of the fluorosilanes are probably in error, (2) a 13—silicon substituted alkyl radical is stabilised by ca 12 kJ mol' and (3) the simplest divalent silicon species, SiR2, has an enthalpy of formation of 273 ± 6 kJ mo11, some 30 kJ mo11 higher than earlier estimates. INTRODUCTION Traditional methods of determining thermodynamic quantities centre on calorimetry and the study of equilibria (ref. 1,2). These methods are appropriate for pure stable compounds and clean reactions but are not generally possible for reactive species of lower (or higher) valence states than those commonly encountered. An approach which has proved useful for such species is that based on a variant of the equilibrium law, viz, the principle of microscopic reversibility (see e.g. ref. 3). In a reversible process such as