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If the complete reaction of 45.0 g of B(s) requires 74.93 kJ of heat to be...

If the complete reaction of 45.0 g of B(s) requires 74.93 kJ of heat to be absorbed from the surroundings, what is the enthalpy change of the following equation in kJ/molrxn? 2B(s) + 3H2(g) -> B2H6 (g) ∆H rxn = ? kJ/molrxn

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Answer #1

2B(s) + 3H2(g) ---------------------------> B2H6 (g)

21.62 g B -----------------------> kJ

45.0 g B ---------------------------> 74.93 kJ

heat needed for the reaction = 74.93 x 21.62 / 45.0

                                               = 36.0 kJ /mol

∆H rxn = 36.0 kJ /mol

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