Question

Calculate the standard enthalpy change for the reaction of dissolving 5.00 grams of NaOH in 100.0 mL of water at 25°C, given that the heat absorbed by the solution is 11.76 kJ. (Assume the density of water is 1.00 g/mL and the heat capacity of the solution is the same as that of water.)

Answer 1

To calculate the standard enthalpy change for the reaction, we first need to determine the moles of NaOH dissolved and then use the heat absorbed by the solution to find the enthalpy change per mole of NaOH.1. Calculate the moles of NaOH:The molar mass of NaOH = 22.99 g/mol  Na  + 15.999 g/mol  O  + 1.007 g/mol  H  = 39.996 g/molmoles of NaOH =  5.00 g  /  39.996 g/mol  = 0.125 mol2. Calculate the heat absorbed per mole of NaOH:q = heat absorbed by the solution = 11.76 kJq_per_mole = q / moles of NaOH =  11.76 kJ  /  0.125 mol  = 94.08 kJ/mol3. Calculate the standard enthalpy change for the reaction:The standard enthalpy change for the reaction  H  is equal to the heat absorbed per mole of NaOH.H = 94.08 kJ/molTherefore, the standard enthalpy change for the reaction of dissolving 5.00 grams of NaOH in 100.0 mL of water at 25C is 94.08 kJ/mol.