To calculate the enthalpy change when 50 g of NaOH is dissolved in 500 mL of water at 25C, we need to consider the following steps:1. Calculate the moles of NaOH.2. Use the standard enthalpy of formation values for NaOH and H2O.3. Calculate the enthalpy change using the moles of NaOH and the enthalpy of formation values.Step 1: Calculate the moles of NaOHThe molar mass of NaOH = 22.99 Na + 15.999 O + 1.007 H = 39.996 g/molMoles of NaOH = mass / molar mass = 50 g / 39.996 g/mol = 1.250 molStep 2: Use the standard enthalpy of formation valuesThe standard enthalpy of formation of NaOH aq = -469.15 kJ/molThe standard enthalpy of formation of H2O l = -285.83 kJ/molStep 3: Calculate the enthalpy changeThe dissolution of NaOH in water can be represented by the following reaction:NaOH s NaOH aq The enthalpy change for this reaction can be calculated using the following equation:H = H products - H reactants In this case, the reactant is NaOH s and the product is NaOH aq . Since the enthalpy of formation of NaOH s is considered to be zero by definition for elements in their standard state , the equation becomes:H = H NaOH aq - H NaOH s H = -469.15 kJ/mol - 0 kJ/molH = -469.15 kJ/molNow, we can calculate the enthalpy change for the dissolution of 1.250 mol of NaOH:H_total = H * moles of NaOHH_total = -469.15 kJ/mol * 1.250 molH_total = -586.44 kJTherefore, the enthalpy change when 50 g of NaOH is dissolved in 500 mL of water at 25C is approximately -586.44 kJ.