To calculate the standard enthalpy change for the dissolution of 5g of sodium chloride in 100mL of water at 25C, we first need to determine the number of moles of NaCl being dissolved.The molar mass of NaCl is 58.44 g/mol 22.99 g/mol for Na + 35.45 g/mol for Cl .Now, we can calculate the number of moles of NaCl:moles of NaCl = mass / molar massmoles of NaCl = 5g / 58.44 g/molmoles of NaCl 0.0856 molNow that we have the number of moles of NaCl, we can use the molar enthalpy of dissolution to calculate the standard enthalpy change:H = moles of NaCl molar enthalpy of dissolutionH = 0.0856 mol -3.9 kJ/mol H -0.333 kJThe standard enthalpy change for the dissolution of 5g of sodium chloride in 100mL of water at 25C is approximately -0.333 kJ.