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

Answer 1

It would get colder

Step-by-step explanation:

The lattice energy is the energy involved in the disruption of interactions between the ions of the salt. In this case, we have: ΔHlat = 350 kJ/mol > 0, so it is an endothermic process (the energy is absorbed).

The solvation energy is the energy involved in forming interactions between water molecules and the ions of the salt. In this case, we have: ΔHsolv = 320 kJ/mol > 0, so it is an endothermic process (the energy is absorbed).

The dissolution process involve both processes: the disruption of ion-ion interactions of the salt and the solvation process. Thus, the enthalphy change (ΔHsol) in the preparation of the solution is calculated as the addition of the lattice energy and solvation energy:

ΔHsol= ΔHlat + ΔHsolv = 350 kJ/mol + 320 kJ/mol = 370 kJ/mol

370 kJ/mol > 0 ⇒ endothermic process

Since the preparation of the solution is an endothermic process, it will absorb energy from the surroundings, so the solution would get colder.