Selected"best" values are given for the heats of combustion (in oxygen to form gaseous carbon dioxide and liquid water) and the heats of formation (from the elements solid carbon, graphite, and gaseous hydrogen) for methane and ethane in the gaseous state, and for all the paraffin hydrocarbons from propane through the octanes and the normal paraffins through eicosane, in both t he liquid (except for one octane which is solid) and gaseous states, all at 25° C. Equations are given for calculating values for all the normal paraffins above eicosane.

A procedure is outlined and utilized for determining with high precision the ratios of the heats of combustion, and hence the heats of isomerization, of the five hexanes. In principle, the r atio of the heats of combustion of any two isomers was determined as the inverse ratio of the masses of carbon dioxide whose formation in the combustion of the respective hexanes produced identical increases of temperature in the calorimeter system, measured as an increase in the resistance of the platinum resistance thermometer.The following values were obtained for the liquid state at 25° C, and calculated to the gaseous state at 25° C and 0° K: Heat of isomerization, 6HFor n-CaHu=i-CaHu I somer Liquid Gas 25° C 25° C 0° K kcal/mole kcal/mole kcal/mole n-Hexane _________ ____ 0 0 0 2-Methylpentane ____

The heats of co mbustion of ten C4 hydrocarbons were meas ured b y combustion of t he gaseous hydrocarbon in a flame at constant pressure in a glass reaction vessel in a calorimeter. The calorimeter system was calibrated by means of electrical e ne rgy.The exp erimental data yielded the following values for the standard heat of combustion, -t:J.Hco , at 25° C and co nstant press ure, of the gaseous hydrocarbon in gaseous oxygen to form gaseo us carbon dioxide and liquid wate r, with all t he reactants and products in their thermodynamic standard reference states, in k cal/mole : n-butane, 687 .42 ± O.15 ; 2-methylpropane, 68S.37 ± O.11 ; I-butene, 649.33 ± O.18 ; cis-2-bute ne, 647.6S ± O.29 ; trans-2-butene, 646.90 ± O.23 ; 2-methylprope ne, 645.19 ± O.2S ; 1,2-butadiene, 619.93 ± O.13 ; 1,3-butadiene, 607.16 ± O.18 ; I-butyne, 620.64 ± O.20 ; 2-buty ne, 61S.84 ± O.23 .Values of hea ts of isomerization, formation, and hydrogenation were derived from these dat a .

The heats of combustion of benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene, n -propylbenzene, and styrene were measured with a bomb calorimeter.The following values were obtained for the heat of combustion, at 25° C and constant pressure, of the liq uid hydrocarbon in gaseous oxygen to form gaseous carbon dioxide and liquid water, with all the r eactants and products in their thermodynamic standard reference states, in international kilojoules per mole: Benzene,3267.09 ±0043; tolU ene, 3909.31 ± 0 049; ethylbenzene, 4564.09 ± 0.72 ; o-xylene, 4552.10 ± 1.02 ; m-xylene, 4551.10 ± 0.62; p-xylene'w4552.09 ± 0.91 ; n-propylbenzene, 5217.37 ± 0.68 ; styrene 4394.14 ± 0.82.ith the factor 1/4.1833, the corresponding values in kilocalories per mole are b enzene, 780.98

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