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.
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
On the other hand, when a
Therefore, the answer is B) - the formation of a