Thermochemistry

Question

The value of ̇△H° for the reaction below is -72 kJ. ________ kJ of heat are released when 5.5 mol of HBr is formed in this reaction.

H2 (g) + Br2 (g) => 2HBr (g)

A) 0.44

B) -72

C) 72

D) 144

E) 198

Answer 1

H₂ (g) + Br₂ (g) ==> 2HBr (g) ... ∆H = -72 kJ

From this balanced equation, and the associated ∆Hrxn, we see that TWO moles HBr formed is associated with the generation of 72 kJ of heat. So, it is easy to find the kJ of heat associated with 5.5 moles of HBr.

5.5 moles HBr x -72 kJ/2 moles HBr = - 198 kJ of heat (note the negative sign since it is exothermic). This would be option (E) except it should have a - sign)