The thermodynamic properties [HO -H~, (Go-H~) IT, (HO -H~)IT, SO, Cpo, llHr, IiGl o , and log KlJ for methanoic (formic) and ethanoic (acetic) acid monomers and dimers in the ideal gaseous state over the temperature range from 0 to 1500 K at 1 "atmhave been calculated by the statistical thermodynamic method using the most recent and reliable molecular and spectroscopic constants. The internal rotational contributions of -OR and -CHa rotors to the thermodynamic properties were evaluated based on internal rotation partition functions formed by summation of calculated internal rotation energy levels. On an assumption that the vapor contains only monomers and dimers, the thermodynamic properties for the monomer-dimer equilibrium mlYtIlTe of meth:moir. lind ethl'ITIoi('. lIeid" in idelll gll!':eOll!': !':tllte were derived. The Te!':ult!': are in agreement with available experimental data.

The ideal gas thermodynamic properties of forty-four key organic oxygen compounds in the carbon range C 1 to C 4 have been calculated by a statistical mechanical technique. The properties determined are the heat capacity (C;), entropy {S' (T)-S' (O)}, enthalpy {Jr (T)-Jr (O)}, and Gibbs energy function {Go (T)-Jr (O)} IT. The calculations have been performed, in most cases, over the temperature range 0 to 1500 K and at 1 bar. The contributions to the thermodynamic properties of compounds having internal-or pseudo-rotations have been computed by employing a partition function formed by the summation of the internal rotational or pseudorotational energy level for each rotor in the given molecule. These energy levels have been calculated by solving the wave equation using appropriate barrier heights, rotational constants, and potential functions for the given rotations. The thermodynamic properties have been calculated using a rigid-rotor. and harmonic-oscillator molecular model for each species. The sources of molecular data and the selection of the values used in the calculation are described. The calculated C; and {S' (T)-SO (O)} values are compared with experimental results where appropriate.

The thermodynamic properties (Cpo, So, Ho−H0o, (Ho−H0o)/T,−(Go−H0o)/T, ΔHfo, ΔGfo and log Kf) for ethane and propane in the ideal gaseous state in the temperature range from 0 to 1500 K and at 1 atm were calculated by statistical thermodynamic methods based on a rigid-rotor harmonic-oscillator model. The internal rotation contributions to thermodynamic functions were evaluated by using a partition function formed by summation of internal rotation energy levels. The calculated heat capacities and entropies compare favorably with available experimental data.

A survey of the published values of heat capacity and enthalpy obtained from calorimetric measurements on the crystal, glass, and liquid phases of the first few members of homologous series expressed as polynomial functions of temperature were fit to selected data by a least squares procedure. Tables of smoothed values of thermodynamic properties, derived from these functions, are presented for 38 compounds.

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