Heat of combustion of isobutane

The data of the present investigation yield for the heat evolved in the combustion of gaseous isobutane in oxygen to form gaseous carbon dioxide and liquid water, at 25° C and a constant pressure of 1 atmosphere, the value 2871.06 ± 0. 53 intern ational kiloj oules per mole.With the factor 1/4.1833, this value becomes 686,31 ± 0.13 kilocalories per mole.The isobutane used was estimated to be of such purity that its heat of combustion would differ from that of an a bsolutely pure sample by less than 0.01 percent.The only previous det ermin atio n of the heat of combustion of isobutane was that made by Thomsen over 50 years ago on some impure material.From these new data values are computed for the heat of formation of isobut.ane."Vhen combined with the previoll sly r eported datlt on the h eat of combu stion of normal butane, the present data yield for the r eaction, n-C,H ID (gas) = i so-C,H ID (gn,s), at 25° C and 1 atmosphere, tJ.H= -6.82 ± 0.63 kilojoules, or -1.63 ± 0.15 kilo calorics, pCI' mole.