The molar heat of solution of NaOH is -445,100 J/mol. To compute much heat (in J) will be released if 40.00 g of NaOH are dissolved in water, we first convert the given grams of NaOH to moles of NaOH, and use the given molar heat of solution to compute for the energy. (Using dimensional analysis):
40 g NaOH x (1 mol NaOH/ 40 g NaOH) x (-445100 J / 1 mol NaOH) = -445100 J of energy.