To calculate the heat of hydration for sodium sulfate Na2SO4 , we need to consider the enthalpy of solution for sodium sulfate and the enthalpy of hydration for water.The enthalpy of solution for sodium sulfate is -138 kJ/mol, which means that 1 mole of sodium sulfate releases 138 kJ of energy when it dissolves in water.Since 3 moles of water are released when 1 mole of sodium sulfate dissolves in water, we need to consider the enthalpy of hydration for water, which is -286 kJ/mol. This means that 1 mole of water releases 286 kJ of energy when it hydrates a substance.Now, we can calculate the heat of hydration for sodium sulfate:Heat of hydration Na2SO4 = Enthalpy of solution Na2SO4 + 3 moles of water * Enthalpy of hydration water Heat of hydration Na2SO4 = -138 kJ/mol + 3 * -286 kJ/mol Heat of hydration Na2SO4 = -138 kJ/mol + -858 kJ/mol Heat of hydration Na2SO4 = -996 kJ/molTherefore, the heat of hydration for sodium sulfate Na2SO4 is -996 kJ/mol.