Using the bond energies below, what is the enthalpy change for the reaction H₂ + Cl₂ → 2HCl?
H–H: 436 kJ/mol, Cl–Cl: 242 kJ/mol, H–Cl: 431 kJ/mol

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Question

Using the bond energies below, what is the enthalpy change for the reaction H₂ + Cl₂ → 2HCl?
H–H: 436 kJ/mol, Cl–Cl: 242 kJ/mol, H–Cl: 431 kJ/mol

Accepted Answer

A: −184 kJ/mol — Energy in (breaking bonds): 436 + 242 = 678 kJ/mol. Energy out (forming bonds): 2 × 431 = 862 kJ/mol. ΔH = 678 − 862 = −184 kJ/mol. The negative sign confirms the reaction is exothermic. Students commonly forget to multiply the H–Cl bond energy by 2.

Answer

B: +184 kJ/mol

Answer

D: +678 kJ/mol

Answer

C: −862 kJ/mol

Answer

A: −184 kJ/mol

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