The lattice enthalpy of sodium hydroxide is less than the sum of hydration enthalpies of hydroxide ions and sodium ions.
Explanation:
Lattice enthalpy is defined as heat energy required to break 1 mole of crystal lattice.
Hydration enthalpy is defined as amount energy released when 1 mole of ions undergo hydration (surrounding of water molecules).It is always negative.
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.
The rise in temperature is due to hydration enthalpy of hydroxide ions and sodium ions is greater than that of the lattice enthalpy of the sodium hydroxide. This is the reason behind the warmth of the sodium hydroxide solution.
