The gas-phase equilibrium between trioxan and formaldehyde: the standard enthalpy and entropy of the trimerisation of formaldehyde

Abstract

Equilibrium constants for the reaction (1) have been measured in the temperature range 72–108°. The results 3H₂CO(g)⇌ C₃O₃H₆(g)(1) can be expressed by equation (2). The standard enthalpy and entropy changes at 25° for the trimerisation of log (K_p, m.⁴ kN^–2= 7·35 ± 0·11)× 10³/T–(23·8 ± 0·6)(2) gaseous formaldehyde to form solid trioxan, are ΔH°₂₉₈=–194·0 ± 2·5 kJ(mole trioxan)^–1 and ΔS°₂₉₈=–526 ± 13 J deg.^–1(mole trioxan).^–1 The value of ΔH°₂₉₈ is more precise than that calculated from exiting combustion data but is in general agreement. ΔS°₂₉₈ agrees well with the value calculated from spectroscopic and heat-capacity data.