Bond enthalpies Quiz
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5 questions, one answer each
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1. Which is the correct formula for ΔH using bond enthalpies?
- A. Σ formed – Σ broken
- B. Σ broken + Σ formed
- C. Σ broken – Σ formed
- D. Σ broken × Σ formed
2. Using H–H 436, Cl–Cl 243 and H–Cl 432 kJ mol⁻¹, what is ΔH for H₂ + Cl₂ → 2HCl?
- A. +185
- B. –679
- C. +679
- D. –185
3. Why is a bond enthalpy calculation only an estimate?
- A. Bond enthalpies are always negative
- B. It uses mean values that are not exact for the molecules involved
- C. Bonds never break in reactions
- D. It ignores the number of moles
4. A bond has a very low bond enthalpy. What does this suggest about its reactivity at room temperature?
- A. It breaks easily so reactions are faster
- B. It is unreactive
- C. It forms more strongly
- D. It cannot break
5. The enthalpy change for CH₄(g) → C(g) + 4H(g) is +1664 kJ mol⁻¹. What is the mean C–H bond enthalpy?
- A. 6656
- B. 1664
- C. 832
- D. 416