Entropy of isoprene from heat-capacity measurements

Abstract

Measurements of heat capacity were made on a sample of isoprene of high purity from 20 to 300 0 K with an adiabatic vacuum-type calorimeter. At 200K the heat capacity of the crystalline material was found to be U.8 j/(mole ' degree), and with increase in temperature the heat capacity increases, following the usual type of curve for crystalline substances. At lOO°l( the heat capacity of the solid is 64.7 j/(mole· degree), and at the melting point, 126.4°l(, the heat of fusion is determined to be 4,830 ± 15 j/mole. The heat capacity of the substance increases about 60 percent during the change from solid to liquid. Above the fusion temperature the curve is characteristic of liquids, and the heat capacity attains a value of 152.6 j/(mole . degree) at 298.2°K (25°C). Utilization of the data, according to the third law of thermodynamics, yields 229.3 ± 1.0 jf (mole· degree) for the entropy of isoprene at this temperature.

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

“…There is an experimental entropy available for comparison with our result for 2-methyl-l,3-butadiene (isoprene). The experimental value, 75.2 ± 0.3, [24,25] is 0.5 cal/deg mole lower than the value given by the increment equation without the term -0.3. Although this difference is well within the expected uncertainties of the method, the additional constant term (-0.…”

Heat of combustion of isoprene

“…In previous papers data have been reported on the heat of combustion [8]1 and on the entropy and free energy of formation of rubber hydrocarbon [1]. Recently, data on the entropy of isoprene have been reported by Bekkedahl and Wood [2], who discuss the chemical similarity of isoprene and rubber hydrocarbon, and point out the desirability of a knowledge of the free energy of forma-I Numbers in brackets relate to the literature references given at the end of this paper. 589 tion of isoprene for use in studying the thermodynamics of reactions involving the two substances.…”

Specific heat of the synthetic rubber Hycar O.R from 15 to 340 K

“…It was similar to the apparatus previously used to determine the specific heat of rubber [4] and of isoprene [5], with some alterations intended to increase the convenience and facility of the measurements.…”

“…(oil-resistant) synthetic rubber is a continuation of a program started some years ago at the National Bureau of Standards, the object of which is to furnish thermodynamic data on various types of rubber, both natural and synthetic, and the monomers from which they are polymerized. Such data have been obtained for unvulcanized natural rubber [4] 1 and its monomer, isoprene [5], and the equilibrium relationship between the two has been studied [2]. In the present paper, specific heat measurements on synthetic rubber Hycar O.R.…”