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# Diborane is a potential rocket fuel which undergoes combustion according to the equation B2H6(g) + 3O2(s) → B2O3(s) + 3H2O(g) Calculate the enthalpy change for the combustion of diborane. Given

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Diborane is a potential rocket fuel which undergoes combustion according to the equation

B2H6(g) + 3O2(s) → B2O3(s) + 3H2O(g)

Calculate the enthalpy change for the combustion of diborane. Given

(i) 2B(s) + 3/2O2(g) → B2O3(s); ΔH = -1273 kJ per mol

(ii) H2(g) + 1/2O2(g) → H2O(l); ΔH = -286 kJ per mol

(iii) H2O(l) → H2O(g); ΔH = 44 kJ per mol

(iv) 2B(s) + 3H2(g) → B2H6(g); ΔH = 36 kJ per mol

(a) +2035 kJ per mol

(b) -2035 kJ per mol

(c) +2167 kJ per mol

(d) -2167 kJ per mol

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Correct answer: (b) -2035 kJ per mol

Explanation:

For the equation

B2H6(g) + 3O2(s) → B2O3(s) + 3H2O(g)

Eqs. (i) + 3(ii) + 3 (iii) - (iv)

ΔH = -1273 + 3(-286) + 3(44) - 36

= -1273 - 858 + 132 - 36

= -2035 kJ/mol

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