For an anhydrous ionic compound Z, the following thermodynamic data are obtained for its dissolution in water at 298 K.
Enthalpy contributions (kJ mol⁻¹):
• Solvent reorganization around the ions: +5
• Hydration of the ions: −50
• Disruption of the ionic crystal lattice: unknown
Entropy contributions (J mol⁻¹ K⁻¹):
• Disruption of the ionic crystal lattice: +10
• Solvent reorganization around the ions: +30
• Hydration of the ions: +90
The experimentally measured standard free energy change for dissolution of compound Z at 298 K is −25 kJ mol⁻¹.
Complete the tasks below, showing all reasoning and calculations.
(a) Determine the overall standard entropy change for the dissolution of compound Z. Report the value in J mol⁻¹ K⁻¹.
(b) Using the overall entropy change from part (a) and the measured free energy change, calculate the unknown standard enthalpy contribution for disruption of the ionic crystal lattice.
(c) Evaluate whether the magnitude of the lattice enthalpy you obtained in part (b) is chemically reasonable in comparison with the hydration enthalpy, and explain what this implies about the driving force for dissolution of compound Z.