Heat of formation of boron trichloride

The heat of formation of gaseou boron t richlorid e has been determined by t he d irect reaction of gaseous chlorin e with am orphous bor on i n a calorimete r.B (amorph) + 3/2 CIz (gas) = BCh (gas) AHfO(25° C)= -407.98 ± 1.34 k j/mole (-97.51 ± 0.32 k cal/m oJe) .By utilizing t he valu es previously reported for the h ea ts of formation of boric acid, diboran e, a nd pe ntaborane, t he heat of h yd rolysis of boron t richloride and t he h eat s of react ion of d ibora ne a nd p entaboran e wit h chlorine have been obtai ned .By t h e u se of an estimat ed value for t he h eat of sublimation of boron , t he average bond energy of t he B-CI bond in boron t richlorid e is fo und to be 105. 2 k cal at 0° K .The d ata on t he h eats of formation of diborane, bor ic oxide, boric acid, a nd boro n trichloride now form a co nsistent set of values.