Gaseous Heat Capacities. II

Abstract

The present paper describes a continuation of the work on the heat capacities of lower hydrocarbons by the Lummer-Pringsheim adiabatic expansion method. The apparatus and the procedure described in the first paper of this series, henceforth to be denoted as Part I, was used in the present research without important modifications.

Heats, equilibrium constants, and free energies of formation of the C3 to C5 diolefins, styrene, and the methylstyrenes

“…The uncer tainty in the calculated values of the thermodynamic functions is estimated to be about 0.2 cal/deg mole at the lower temperatures and somewhat greater at the higher temperatures because of the neglect of vibrational anharmonicities. The values of heat capacity calculated for propadiene in the present investigation agree very well with the experim ental data that have been reported [4,9,10]. Some values of entropy previously calculated for propadiene by other workers [11 , 12], however, differ markedly, for some unknown caUSE: , from those given in the presen t report.…”

Heat content, free-energy function, entropy, and heat capacity of ethylene, propylene, and the four butenes to 1,500 degrees-K

“…A discussion of the following assignment may be found in another report [4). The frequencies are given in wave numbers, cm-1 : lsobutene has the same symmetry as cis-2-butene, C2v, but the presence of both methyl groups are isomorphic and the classifications of the frequencies are quite similar [4]: A threefold cosine type barrier of 1,950 cal/mole, when combined with the previously mentioned constants, was found to give results agreeing satisfactorily with the experimental values of the entropy [5] and the gaseous heat capacity [6].…”

Thermodynamic properties of cis-2-butene from 15 degrees to 1,500 degrees K

“…A frequency assignment for the internal vibrations of cis-2-butene based upon the infrared absorption and Raman spectra reported by Gershinowitz and Wilson [10],2 was used to calculate the barrier restricting internal rotation of the methyl groups from the gaseous specific heat data of Kistiakowsky and Rice [9]. The spectroscopic value for the entropy of cis-butene in the ideal gas state involving this barrier is in good agreement with the experimental value of the entropy determined from the calorimetric data.…”

“…The specific h eat of gaseous cis-2-butene was determined by Kistiakowsky and Rice [9], who used an fi,diabatic expansion method by which the h eat capacity is determined from the change in tem-· perature that results from an isentropic expansion . The equation of state of the gas is important for this method, since, in effect, the specific heat is determined from the ratio of the work done by the gas in the isentropic expansion to the m easured change of temperature, and the work done is calculated with the aid of the equation of state of the gas.…”

“…where V and v are the volumes of the saturated vapor and liquid, respectively, L. is the observed heat of vaporization ( If an equation of state of the form (9) is assumed, values of k may be obtained from the experimental values of p, V, and T . Thus (10) Figure 2 shows the values of k obtained in this way.…”