Accession Number : ADD095065

Title :   Ideal Gas Thermodynamic Properties and Isomerization of n-Butane and Isobutane,

Corporate Author : NATIONAL STANDARD REFERENCE DATA SYSTEM

Personal Author(s) : Chen, S S ; Wilhoit, R C ; Zwolinski, B J

Report Date : Jan 1975

Pagination or Media Count : 18

Abstract : Reported values of structural parameters, vibrational fundamentals, and potential energy functions for internal rotation of n-butane and isobutane are reviewed. The selected values were used to calculate the thermodynamic properties in the temperature range of 0 to 1500 K by the usual statistical thermodynamic methods using the rigid-rotor and harmonic-oscillator model. Contributions of internal rotation were evaluated by the direct sum of terms containing energy levels which were calculated with a one-dimensional potential model. For internal rotation about the central C-C bond in n-butane, energy levels were approximately by two procedures. A unique potential function was assumed for each methyl rotor of n-butane or of isobutane. Top-top interactions in isobutane were approximated by the potential parameter V6 which was determined empirically by comparison with thermodynamic data. The calculated and observed values of heat capacities and entrophies agree well within experimental uncertainties. Standard enthalpies of formation at 298.15 K for the ideal gaseous state were selected from measured values of heats of combustion and third-law enthalpies for isomerization. Corresponding values of delta Hf-delta, delta Gf and log Kf are tabulated over the same temperature range. (Author)

Descriptors :   *BUTANES, *THERMODYNAMIC PROPERTIES, *ISOMERIZATION, *THERMOCHEMISTRY, MOLECULAR STRUCTURE, VIBRATIONAL SPECTRA, POTENTIAL ENERGY, ROTATION, MOLECULAR ENERGY LEVELS, MOMENT OF INERTIA, IDEAL GAS LAW, ENTROPY, SPECIFIC HEAT, ENTHALPY, HEAT OF FORMATION, HEAT OF COMBUSTION, EQUILIBRIUM(GENERAL), TEMPERATURE, STATISTICAL PROCESSES

Subject Categories : Organic Chemistry
      Thermodynamics

Distribution Statement : APPROVED FOR PUBLIC RELEASE