Diborane (B2H6) has been considered as a possible rocket fuel. Calculate DH° for the reaction B2H6 (g) - --> 2B (s) + 3H2 (g) using the following dа ta: DH° (kJ) 2B (s) + 1.5O2 (g) - -> B2O3 (s) - 1273 B2H6 (g) + 3O2 (g) - -> B2O3 (s) + 3H2O (g) - 2035 H2 (g) + O2 (g) - -> H2O (g) - 242 A. DH° = - 36 kJ B. DH° = + 36 kJ C. DH° = - 86 kJ D. DH° = - 86 kJ

A. DH° = - 36 kJ

Explanation:

It is possible to obtain DH° of a reaction by the sum of DH° of half reactions. The DH° of the reaction:

B₂H₆ (g) → 2B (s) + 3H₂ (g)

Could be obtained from:

(1) 2B (s) + 1.5O₂ (g) → B₂O₃ (s) DH° = - 1273kJ

(2) B₂H₆ (g) + 3O₂ (g) → B₂O₃ (s) + 3H₂O (g) DH° = - 2035kJ

(3) H₂ (g) + 0.5O₂ (g) → H₂O (g) DH° = - 242kJ

The sum of (2) - (1) gives:

B₂H₆ (g) + 1.5O₂ (g) → 2B (s) + 3H₂O (g) DH° = - 2035kJ - (-1273kJ) = - 762kJ

Now, this reaction - 3 * (3):

B₂H₆ (g) → 2B (s) + 3H₂ (g) DH° = - 762kJ - (3*-242kJ) = - 36kJ

Thus, right answer is:

A. DH° = - 36 kJ