Question

The Cl-Cl bond energy is 243 kJ/mol. Therefore the formation of a single bond between chlorine atoms ? A) should require the absorption of 243 kJ per mole of `Cl_2` formed. B) should result in the release of 243 kJ per mole of `Cl_2` formed.

Answer 1

The bond energy, or bond enthalpy, expresses the energy needed to break a chemical bond, that's why it will always be listed as a positive value.

In your case, 243 kJ of energy are required to break the `"Cl-Cl"` bond per mole of `Cl_2` molecules.

On the other hand, when a `"Cl-Cl"` bond is formed, 243 kJ of energy are released per mole of `Cl_2` molecules.

Bond making is an exothermic process, while bond breaking is an endothermic process.

Therefore, the answer is B) - the formation of a `"Cl-Cl"` bond will release 243 kJ per mole of `Cl_2` formed.