The heat of formation of boron trichlorid e has
long been uncertain because of the fact that calculation
of it has been depend ent upon uncertain values
of the heat of formation of boric oxide or boric acid . Since new values have been determined for the heaL
of formation of boric oxide through Lhe heat of de- composition of diboran e [1] 2 and the heat of r eaction
of diborane with water [2], it seemed desirable
to make a direct determination of Lhe hea t of formation
of boron trichloride. This latter value,
when combined with the heat of hydrolysis of boron
trichloride and with auxiliary data, yields an inde- pendenL value for the heat of formaLion of boric
oxide. The consistency in the values t hus obtained
is very strong evidence for the accuracy of the heaLs
of formation of boric oxide, boric acid, diborane, and
boron trichlorid e.
An accurat e valu e Jor th e heat of formation of
BCla provides useful information r egarding th e energy
of the B-Cl bond and permiLs t ile calculation of
the heat of r eaction of boron hydrides with chlorin e.