formaldehyde - Sciencemadness Dot Org

MO HOMERIC FORMALDEHYDE 21
CGraphite (Rossini) + Hs -h l/202 -* CHoO(g) -f 28 keaL
The heat of combustion of the monomelic gas was determined by von
Wartenberg and Lemer-Steinberg 28 in 1925 as 134.1 kcaL
CHsO (g) -f 0*-*H30 (liq.) -J- C02 4-134.1 keaL
The heat of formation as calculated from this figure, using Rossini's recent
values 23 for the heats of formation of carbon dioxide (94.03 kcal) and water
(68.31 kcal) at 1&°C, is 28.3 kcal per mol, or 28.5 kcal as based on the
beta-graphite standard. Calculation of the heat of formation from the
I.C.T. value 11 for the free energy of carbon monoxide, based on equilibrium
measurements and the Newton and Dodge formula 15 for the variation of
the carbon monoxide-hydrogen-formaldehyde equilibrium with temperature,
gives a value of 27.7 kcal at 18°C (corrected to the newer Rossini
standards mentioned above) which serves as an independent check on the
von Wartenberg value. This confirmation is important because von
Wartenberg, Muehlinski, and Riedler 37 had previously published an extremely
erratic value (4.0 kcal) for the heat of formation of formaldehyde -
Values for the heat of formation of formaldehyde at various temperatures
can be readily calculated by means of equilibrium data. However^
since variation with temperature is less than 1 kcal in the range 18 to 700 D C7
and since the accuracy of available data does not permit us to express the
heat of formation figure in fractions of a kcal, variations from the 2S kcal
value may be disregarded as negligible within these limits.
In 1897 Delepine 4 reported that the heat of formation of formaldehyde
was 25.4 kcal. This figure, determined indirectly from the heat of combustion
of hexamethylenetetramine and the heat of reaction of formaldehyde
and ammonia, is naturally less accurate than the later measurements.
Recalculated on the basis of Rossini's values, this figure becomes 24.7
kcals.
The free energy of formaldehyde, based on the most accurate data now
available, should be taken as —27 kcal per gram mol at 25 °C. When this
figure is calculated from the I.C.T. value for the free energy of carbon
monoxide and the Newton and Dodge equilibrium measurements for the
reaction CO + H^