Pentaborane b5h9 (s) burns vigorously in o2 to give b2o3 (s) and h2o (l). what is δh° for the combustion of 1 mol of b5h9 (s) ? substance δh°f (kj/mol) b2o3 (s) - 1273.5 b5h9 (s) + 73.2 h2o (l) - 285.8

Write a balanced chemical equation

2B5H9 + 12O2 - - - > 5B205 + 9 H20

From the Hess law wich state that regardless of the multiple steps of chemical reaction the total enthapy is equal to the sum of all changes

hence;

{ (5 x - 1273.5) + (9 x - 289.8) } - { (73.2 x2) + (0 x12) } = - 9086.1kj / mol