HEAT OF FORMATION
��In this r6sum6 of thermo-chemistry we do not desire to give too many numerical data. The following tables give the thermo-chemical numbers for a few of the most impor- tant series of substances.
The heats of combustion and formation are given for the temperature 16°, under constant pressure and starting from carbon in the form of diamond.
��Htdrocabbons
��• Kftme
�Formula
�Heat of Formation
�i Heat of Combustion
� �Gas
�Liquid
�Methane .
� �213-5 Cal.
�Ethane .
� �372-3 „
�Propane . Butane, normal
� �528-4 „ i 687-2 „
�Hexane, normal
�i
�j 991-2 „
�Di-isopropane .
�CfiHn
� �| 998-9 „
�Ethylene . Propylene Isobutylene
�C-jH,
� �3411 „
499-3 „
1 650-2 „
�Amylene (ordinary) .
� �| 811-3 „
�Acetylene
�CgHg
� �■ 315-7 „ is, according to Berthelot, equal to (94-8 x 2) + (69 x 8) = Cal., therefore the difference 28*8 Cal. represents the heat of formation of this hydrocarbon.
We may notice that in the case of the saturated hydro- carbons a difference of CH 2 in the molecular constitution corresponds to an almost constant difference of 158 Cal. in the heat of combustion. A similar regularity is noticed in the case of other homologous series.
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