To calculate the standard enthalpy change when 5 grams of sodium chloride NaCl dissolves in 100 mL of water at 25C, we need to know the enthalpy of solution for NaCl. The enthalpy of solution is the amount of heat absorbed or released when a solute dissolves in a solvent at a constant pressure.The enthalpy of solution for NaCl is approximately -3.88 kJ/mol.First, we need to convert the mass of NaCl to moles:5 g NaCl * 1 mol NaCl / 58.44 g NaCl = 0.0856 mol NaClNow, we can calculate the enthalpy change:H = moles * enthalpy of solutionH = 0.0856 mol * -3.88 kJ/mol = -0.332 kJThe standard enthalpy change when 5 grams of sodium chloride dissolves in 100 mL of water at 25C is approximately -0.332 kJ.