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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.

H_{2}(g) + Br_{2}(g) \rightarrow 2HBr(g)

Given that Bond energy of H_{2}Br_{2} and HBr is 435 kJ mol-1 , 192 kJ mol-1 and 368 kJ mol–1 respectively.

Answers (1)

We know that to calculate Enthalpy change, the formula is

= (Bond energy of H-H bond + Br-Br bond) – (2 × bond energy of H-Br)

In our case, we can calculate enthalpy change by substituting the values.

= (435 + 192) kJ mol^{-1} - (2 \times 368) kJ mol^{-1}

= -109 kJ mol-1

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