Enthalpy of solution and hydrationAQA A-Level Chemistry: Mind map

Exam questions on Enthalpy of solution and hydration

1. A student is studying what happens when the ionic solid sodium chloride dissolves in water. The process can be considered in two stages: the ionic lattice is first broken up into gaseous ions, and the gaseous ions are then surrounded by water molecules.
   Define the term enthalpy of hydration.2 marks
2. The enthalpy of solution of sodium chloride is found using an enthalpy cycle. Data (kJ mol⁻¹): enthalpy of lattice formation of NaCl = −787; enthalpy of hydration of Na⁺(g) = −406; enthalpy of hydration of Cl⁻(g) = −364.
   Calculate the enthalpy change when 5.85 g of sodium chloride (Mr = 58.5) dissolves in water. State whether the energy is released or absorbed.2 marks
3. Magnesium chloride dissolves in water. Data (kJ mol⁻¹): enthalpy of lattice dissociation of MgCl₂ = +2526; enthalpy of hydration of Mg²⁺(g) = −1920; enthalpy of hydration of Cl⁻(g) = −364. The enthalpy of hydration of Na⁺(g) is −406 kJ mol⁻¹.
   Calculate the enthalpy of solution of magnesium chloride.3 marks