To calculate the enthalpy change of dissolution, we first need to determine the number of moles of sodium chloride NaCl that are being dissolved. The molar mass of NaCl is approximately 58.44 g/mol 22.99 g/mol for Na and 35.45 g/mol for Cl .Now, we can calculate the number of moles of NaCl:moles of NaCl = mass of NaCl / molar mass of NaClmoles of NaCl = 5 g / 58.44 g/molmoles of NaCl 0.0856 molNext, we can use the molar enthalpy of dissolution to calculate the enthalpy change:enthalpy change = moles of NaCl molar enthalpy of dissolutionenthalpy change = 0.0856 mol -3.9 kJ/mol enthalpy change -0.333 kJSo, the enthalpy change of dissolution when 5 grams of sodium chloride dissolves in 100 mL of water at 25C is approximately -0.333 kJ.