Question

Predict whether following reaction will be exothermic or endothermic. Give reason for your answer: H–H (g) + Cl–Cl (g) → 2H–Cl (g)

Answer 1

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Answer 2

"The "chemical reactions" which are evolved heat energy during the formation of products are called exothermic reaction. The chemical reactions which are absorbed from their surroundings during the formation of products are called endothermic reaction.  

The given reaction is as follows.

$H-H(g)\quad +\quad Cl-Cl(g)\quad →\quad 2H-Cl(g)$

Enthalpy of H-H bond and Cl-Cl bond. It is 436 kJ for the H-H bond and 242 kJ for the Cl-Cl bond. Add them and the "energy required" by the system is 678kJ.  

Now the H-Cl bond enthalpy is 431 kJ. The system, therefore, loses 862 kJ of energy, and it is, therefore, an exothermic reaction."