Question

Lattice enthalpy and enthalpy of solution of NaCl are 788 kJmol⁻¹ and 4kJmol⁻¹ respectively. The hydration enthalpy of NaCl is

A. −780kJmol⁻¹
B. 780kJmol⁻¹
C. −784kJmol⁻¹
D. 784kJmol⁻¹

Answer 1

The hydration enthalpy of NaCl is calculated using the lattice enthalpy (788 kJ/mol) and the enthalpy of solution (4 kJ/mol), resulting in a value of −784 kJ/mol, which is option C.

Step-by-step explanation:

To calculate the hydration enthalpy of NaCl, we can use the cycle that relates the lattice enthalpy, enthalpy of solution, and the hydration enthalpy.

The lattice enthalpy is the energy required to separate one mole of an ionic solid into gaseous ions, and it is given as 788 kJ/mol for NaCl.

The enthalpy of solution is the energy change when one mole of an ionic substance dissolves in water, which is 4 kJ/mol for NaCl.

The hydration enthalpy can be found using Hess's law, which states that the total enthalpy change for a reaction is the same, regardless of the pathway taken. The relationship is given by:

Hydration enthalpy = Lattice enthalpy + Enthalpy of solution

Therefore:

Hydration enthalpy of NaCl = (-788 kJ/mol) + (4 kJ/mol) = -784 kJ/mol

Thus, the correct answer is C. −784 kJ/mol.