Editing Openai/69227557-0850-8003-9c19-8f26825e337d (section)

===== For gas-phase atoms: =====

C(g)+3H(g)+Cl(g)→CH3Cl(g)\text{C(g)} + 3\text{H(g)} + \text{Cl(g)} \rightarrow \text{CH}_3\text{Cl(g)}C(g)+3H(g)+Cl(g)→CH3Cl(g)
The total bond energy in CH₃Cl is roughly:
* 3 × C–H bonds ≈ 3 × 410 kJ/mol ≈ 1230 kJ/mol
* 1 × C–Cl bond ≈ 330–340 kJ/mol

Total ≈ 1.5 × 10³ kJ/mol (≈ 1500 kJ/mol).

By definition, bond enthalpy is the energy required to break a bond. So:
* To break CH₃Cl completely into separate atoms, you must put in ~1500 kJ/mol (endothermic).
* Going the other way (atoms → CH₃Cl), the system releases ~1500 kJ/mol (exothermic).

So yes: “~1500 kJ is transferred from the atoms to the bonds” is basically saying

: 

That is not yet a statement about the full reaction you do in the lab.