The standard molar enthalpy of formation of diborane, B₂H₆(g), cannot be determined directly because the compound cannot be prepared by the reaction of boron and hydrogen. It can be calculated from other enthalpy changes, however. The following enthalpy changes can be measured. 

(a) Show how these equations can be added together to give the equation for the formation of B₂H₆(g) from B(s) and H₂(g) in their standard states. Assign enthalpy changes to each reaction.

(b) Calculate ∆_fH° for B₂H₆(g). 

(c) Draw an energy level diagram that shows how the various enthalpies in this problem are related.

(d) Is the formation of B₂H₆(g) from its elements exo- or endothermic?

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4 B(s) + 3 O₂(g) → 2 B₂O3(s) A,H° = -2543.8 kJ/mol-rxn H₂(g) + ¹/2O₂(g) → H₂O(g) A,H° = -241.8 kJ/mol-rxn B₂H6(g) + 3 O₂(g) → B₂O3(s) + 3 H₂O(g) AH = -2032.9 kJ/mol-rxn