Question

The enthalpy of solution for NaOH is -44.46 kJ/mol. What can you conclude about the relative magnitudes of the absolute values of ΔHsolute and ΔHhydration, where ΔHsolute is the heat associated with separating the solute particles and ΔHhydration is the heat associated with dissolving the solute particles in water?

Answer 1

Answer: $\Delta H_{hydration}$ > $\Delta H_{solute}$.

Explanation:

Lattice enthalpy is defined as heat energy required to break 1 mole of crystal lattice.  It is represented as $\Delta H_{solute}$.

Hydration enthalpy is defined as amount energy released when 1 mole of ions undergo hydration (surrounding of water molecules).It is always negative.  It is represented as $\Delta H_{hydration}$.

Enthalpy of solution = Lattice enthalpy + hydration enthalpy

If amplitude of lattice enthalpy > hydration enthalpy , enthalpy of solution will positive.Hence, solution will feel cool.

If magnitude Lattice enthalpy < hydration enthalpy, enthalpy of solution will negative. Hence solution will feel warm or hot.

Reaction between sodium hydroxide and water is an example of an exothermic reaction. During this process sodium hydroxide dissociates into sodium ions and hydroxide ions into the water.  

Thus lattice enthalpy is lesser than the hydration enthalpy.