To calculate the enthalpy of solution, we first need to determine the number of moles of ammonium nitrate NH4NO3 in 5 grams. The molar mass of NH4NO3 is:Molar mass = 14.01 g/mol N * 2 + 1.01 g/mol H * 8 + 16.00 g/mol O * 3 Molar mass = 28.02 g/mol + 8.08 g/mol + 48.00 g/molMolar mass = 80.10 g/molNow, we can find the number of moles of NH4NO3 in 5 grams:moles = mass / molar massmoles = 5 g / 80.10 g/molmoles = 0.06242 molNow that we have the number of moles, we can calculate the enthalpy of solution using the given molar heat of solution:Enthalpy of solution = moles * molar heat of solutionEnthalpy of solution = 0.06242 mol * -25.7 kJ/mol Enthalpy of solution = -1.603 kJThe enthalpy of solution of 5 grams of ammonium nitrate in 100 grams of water at room temperature is approximately -1.603 kJ.