To calculate the standard enthalpy change of the dissolution of 10 grams of sodium chloride NaCl in 250 milliliters of water at 25C, we first need to determine the number of moles of NaCl 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 = 10 g / 58.44 g/molmoles of NaCl 0.171 molNext, we can use the molar enthalpy of dissolution of NaCl -3.9 kJ/mol to calculate the standard enthalpy change for the dissolution of 0.171 mol of NaCl:H = moles of NaCl molar enthalpy of dissolutionH = 0.171 mol -3.9 kJ/mol H -0.667 kJTherefore, the standard enthalpy change of the dissolution of 10 grams of sodium chloride in 250 milliliters of water at 25C is approximately -0.667 kJ.