AQA · OCR A · AS / Year 12
Bond Enthalpy Questions
Count bonds, estimate reaction enthalpies and find missing values. Work through the calculation before checking the answer.
Work it out, then check
Question 1 of 6
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Worked answer
Before the next question
Breaking a bond requires energy; forming a bond releases it. Estimate a reaction enthalpy using the energy required to break the reactant bonds minus the energy released when product bonds form. Use gaseous species when working with mean bond enthalpies.
A worked example
For H₂ + Cl₂ → 2HCl, given H–H = 436, Cl–Cl = 242 and H–Cl = 431 kJ mol⁻¹: ΔH = 436 + 242 − 2(431) = −184 kJ mol⁻¹.