Question

What is the enthalpy change when 25.0 g of potassium chloride is dissolved in 250 mL of water at 25°C? Given that the density of water is 0.997 g/mL and the enthalpy of solution of potassium chloride is -56.7 kJ/mol.

Answer 1

To calculate the enthalpy change, we first need to determine the number of moles of potassium chloride  KCl  being dissolved. 1. Calculate the moles of KCl:Molar mass of KCl = 39.10 g/mol  for K  + 35.45 g/mol  for Cl  = 74.55 g/molGiven mass of KCl = 25.0 gNumber of moles =  mass  /  molar mass Number of moles = 25.0 g / 74.55 g/mol = 0.335 moles of KCl2. Calculate the enthalpy change:Enthalpy of solution of KCl = -56.7 kJ/molEnthalpy change =  number of moles    enthalpy of solution Enthalpy change = 0.335 moles  -56.7 kJ/mol = -18.99 kJThe enthalpy change when 25.0 g of potassium chloride is dissolved in 250 mL of water at 25C is approximately -18.99 kJ.