The lattice energy of a salt is 350 kJ/mol and the solvation energies of its ion

Question

The lattice energy of a salt is 350 kJ/mol and the solvation energies of its ions add up to 320 kJ/mol for the preparation of a 0.50 M solution. In the preparation of this solution would the solution get colder or warmer? What is the driving force for this solution process? The lattice energy of a salt is 350 kJ/mol and the solvation energies of its ions add up to 320 kJ/mol for the preparation of a 0.50 M solution. In the preparation of this solution would the solution get colder or warmer? What is the driving force for this solution process?

Explanation / Answer

Lattice energy is positive value i.e energy required to break apart an ionic solid and convert its component atoms into gaseous ions

Salvation energy is negative value i.e energy released when solvent molecules interact with atoms or ions of solute

now, consider the preparation of 0.5M solution

No of mole of salute = 0.5mole

Lattice energy for 0.5mole = - 350kJ/2=+175kJ

Energy added by solvation = 320kJ/2= - 120kJ

adding these two energies

Net energy = +175kJ - 120kJ = +55kJ

Net energy is negative value, so energy is needed add from surrounding

Therefore, the solution is should be colder

The overall free energy for this process is negative value, this is the driving force for this process.

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