3. The enthalpy of solution of an ionic compound can be calculated from its latt

Question

3. The enthalpy of solution of an ionic compound can be calculated from its lattice enthalpy and the enthalpies of hydration of the individual ions. Use the information shown below to calculate: a. The enthalpy of solution of solid ammonium chloride b. The enthalpy of solution of solid ammonium nitrate Quantity Lattice energy of solid ammonium chloride Lattice energy of solid ammonium nitrate Enthalpy of hydration of the gaseous Enthalpy Change (kJ/mol) 705 -646 307 ammonium On Enthalpy of hydration of the gaseous chloride ion Enthalpy of hydration of the gaseous nitrate ion -381 -314

Explanation / Answer

enthalpy of solution = lattice energy of salt + hydration energy of ions

When a solid is dissolved in water, the lattice energy is to be supplied(absorbed ) , hence lattice energy should be taken with positive sign and the ions get hydrated liberating heat, that is heat hydration are with negative sign.

Q1) enthalpy of solution of solid ammonium chloride

enthalpy of solution = lattice enrgy of NH4Cl + hydrtion energy of NH4+ and Cl-

= +705 -307-381

=+17 kJ/mol

Q2) enthalpy of solution of ammonium chloride = lattice energy of NH4NO3 + hydration energy of NH4+ and NO3- ions

= +646 -307-314

= +25 kJ/mol

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