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? H2(g)+Br2(g)2HBr(g). Given that, bond energy of H2,Br2andHBr is 435kJmol-1192kJmol-1 and 368kJmol-1 respectively.


Given that, bond energy of H2=435kJmol-1
bond energy of Br2=192kJmol-1
bond energy of HBr=368kJmol-1
For the reaction
H2(g)+Br2(g)2HBr(g)
rH=BE(Reactants)-BE(Products)
=BE(H2)+BE(Br2)-2BE(HBr)
=435+192-(2×368)kJmol-1.
=-109kJmol-1