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6 marksEnergetics

CAPE Chemistry Unit 1 · 2007 · Paper 2 · Question 4(c)(i)

The following diagram represents the Born Haber cycle for the formation of compound MX(s). The associated enthalpy changes in kJ mol⁻¹ for the cycle above are as follows: ΔHᵥM(s) = +86; ΔHᵢM(g) = + 408; ΔHᶠ(MX(s)) = -431; ΔHᵈX₂(g) = + 122; ΔHᵉX(g) = -372.

Which enthalpy values correspond to EACH of the stages I, III and IV in the cycle above?

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Other parts of this question

  1. 4(a)State Hess's Law.[1 mark]
  2. 4(b)(i)Define standard enthalpy change of formation.[2 marks]
  3. 4(b)(ii)Define lattice energy.[2 marks]
  4. 4(c)(ii)Calculate the lattice energy of MX(s).[6 marks]
  5. 4(d)Account for the difference in the lattice energy for MgCl₂(s) and NaCl(s).[4 marks]
  6. 4(e)Explain why the molar enthalpy changes for the following reactions have identical values: HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O(l); H₂SO₄ (aq) + 2KOH (aq) →…[2 marks]

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