Question

What is the enthalpy change for dissolving 10 grams of sodium chloride (NaCl) in 100 mL of water at 25°C? The heat capacity of water is 4.18 J/(g·°C) and the enthalpy of formation of NaCl is -411.1 kJ/mol.

Answer 1

To calculate the enthalpy change for dissolving sodium chloride in water, we need to know the enthalpy of dissolution of NaCl. Unfortunately, the enthalpy of formation of NaCl provided  -411.1 kJ/mol  is not the same as the enthalpy of dissolution. The enthalpy of dissolution is the energy change when one mole of a solute dissolves in a solvent.The enthalpy of dissolution of NaCl is +3.88 kJ/mol. Now we can proceed with the calculation.First, we need to determine the number of moles of NaCl in 10 grams:Molar mass of NaCl = 58.44 g/mol  22.99 g/mol for Na + 35.45 g/mol for Cl moles of NaCl =  10 g  /  58.44 g/mol  = 0.1711 molNow, we can calculate the enthalpy change for dissolving 0.1711 mol of NaCl:H =  0.1711 mol  *  +3.88 kJ/mol  = +0.664 kJSo, the enthalpy change for dissolving 10 grams of sodium chloride in 100 mL of water at 25C is approximately +0.664 kJ.