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5. Chemical energetics
A section of Chemistry, 9701
Listing 10 of 306 questions
Potassiumchloride, KCl, and magnesiumchloride, MgCl 2, are both ionic solids. Table 1.1 energy change value / kJ mol–1 standard enthalpy change of solution, , of KCl +15 lattice energy, , of KCl –701 standard enthalpy change of hydration, , of K+ –322 standard enthalpy change of hydration, , of Cl – –364 standard enthalpy change of solution, , of MgCl 2 –155 lattice energy, , of MgCl 2–2493 Complete the energy cycle involving the enthalpy change of solution and the lattice energy of potassiumchloride, KCl, and the relevant enthalpy changes of hydration. Label your diagram. State symbols should be used. KCl  Use the data in Table1.1 to calculate the enthalpy change of hydration of magnesium ions, Mg2+. Show your working.  of magnesium ions, Mg2+ = kJ mol–1 Explain the reasons why the lattice energy of MgCl 2 is more exothermic than the lattice energy of KCl. Define the following terms. enthalpy change of atomisation first electron affinity Explain what is meant by entropy, S. Potassium chloride is very soluble in water at 20 °C. Explain the solubility of potassium chloride by reference to change in entropy, ∆S. Use the Gibbs equation and your answer to to predict whether potassiumchloride is more soluble in water at 20 °C or at 80 °C. Explain your answer. 
9701_w22_qp_43
THEORY
2022
Paper 4, Variant 3
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Questions Discovered
306