Calculation of enthalpy changes of reaction using bond energies
2 marks · EasyCalculate the enthalpy change (ΔH) for the following reaction using the bond energies given below: Bond energies (kJ/mol):
| Bond | Bond energy / kJ mol^{-1} |
|---|---|
| H–H | 436 |
| Br–Br | 193 |
| H–Br | 366 |
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
–57 kJ/mol (±1)
Must show: Bond breaking and bond making energies shown in full working
Also accept: -56 kJ/mol
Common mistakes: Wrong sign; Omission of bond making part
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Correct method showing total energy for breaking and making bonds.
A1 · 1 mark · Final numerical answer –57 kJ/mol, with sign.
Worked solution
Final answer: ΔH = –103 kJ/mol