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Question
The net enthalpy change of a reaction is the amount of energy required to break all the bonds in reactant molecules minus amount of energy required to form all the bonds in the product molecules. What will be the enthalpy change for the following reaction.
\[\ce{H2(g) + Br(g) -> 2HBr(g)}\]
Given that Bond energy of \[\ce{H2, Br2}\] and \[\ce{HBr}\] is 435 kJ mol–1, 192 kJ mol–1 and 368 kJ mol–1 respectively.
Solution
\[\ce{Δ_rH^Θ = ΣB.E_{(reactant)} - ΣB.E_{(product)}}\]
= \[\ce{B.E._{H2} + B.E._{BR2} - 2 × B.E._{HBr}}\]
= 435 + 192 – (2 × 368) kJ mol–1
= – 109 kJ mol–1
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