First, we need to determine the number of moles of sodium hydroxide NaOH in 10.0 g. The molar mass of NaOH is approximately 40.0 g/mol 23.0 g/mol for Na, 16.0 g/mol for O, and 1.0 g/mol for H .moles of NaOH = mass / molar massmoles of NaOH = 10.0 g / 40.0 g/molmoles of NaOH = 0.25 molNow, we can calculate the enthalpy change using the molar enthalpy of dissolution:enthalpy change = moles of NaOH molar enthalpy of dissolutionenthalpy change = 0.25 mol -44.5 kJ/mol enthalpy change = -11.125 kJThe enthalpy change when 10.0 g of sodium hydroxide dissolves in 200 mL of water at 25C is -11.125 kJ.