If the bond enthalpy for a C-C bond is 348 kJ, what will happen when the C-C bond is formed?

The bond enthalpy is the energy required to break a specific bond, generally averaged over a range of compounds. Since energy is required to make the bond, through the law of conservation of energy, it follows that the same magnitude of energy must be released when the bond is formed. Therefore when a mole of C-C bonds are formed, 348 kJ of energy is released.