The Molecular Accountant
Bond energy calculations — where chemistry becomes bookkeeping. Every bond you break costs energy. Every bond you make earns it back. The profit or loss? That's ΔH.
💡 The Core Idea: The Tug-of-War Ledger
Think of a bond as a stubborn friendship. Breaking it apart takes effort (energy IN). But forming a new bond releases energy OUT — like snapping a spring shut. The net energy change is just the difference.
🔬 Interactive Bond Ledger
Click each bond row to add it to the ledger — just like a real calculation!
🏭 The Chlorine Factory — a huge vat of hydrogen and chlorine gas about to ignite.
Step 1: Bonds BROKEN (Energy IN)
Bond breaking is endothermic — you PUT energy in.
Step 2: Bonds MADE (Energy OUT)
Bond making is exothermic — energy is RELEASED.
📋 Bond Energy Data Table
H–H
436 kJ/mol
Cl–Cl
242 kJ/mol
H–Cl
431 kJ/mol
C–H
413 kJ/mol
O=O
498 kJ/mol
C=O
805 kJ/mol
O–H
464 kJ/mol
📝 Examiner Keywords — Score Every Mark
Bond breaking is endothermic — energy is absorbed from surroundings.
Bond making is exothermic — energy is released to surroundings.
A negative ΔH = exothermic overall (more energy released than absorbed).
Always include units: kJ/mol — not kJ, not kj/mol.
Bond energies are for one mole of bonds. Always multiply by the number of bonds!
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