Question

Calculate the enthalpy change for dissolving 10 grams of potassium chloride (KCl) in 200 mL of water, assuming the temperature remains constant at 25°C. The molar mass of KCl is 74.5513 g/mol and the specific heat capacity of water is 4.184 J/g·°C.

Answer 1

To calculate the enthalpy change for dissolving potassium chloride in water, we need to know the enthalpy of dissolution for KCl. The enthalpy of dissolution is the amount of heat absorbed or released when a substance dissolves in a solvent at constant pressure. For potassium chloride, the enthalpy of dissolution is +17.22 kJ/mol.First, let's determine the number of moles of KCl in 10 grams:moles of KCl = mass / molar massmoles of KCl = 10 g / 74.5513 g/molmoles of KCl = 0.134 molNow, we can calculate the enthalpy change for dissolving 0.134 mol of KCl:H = moles  enthalpy of dissolutionH = 0.134 mol  17.22 kJ/molH = 2.31 kJThe enthalpy change for dissolving 10 grams of potassium chloride in 200 mL of water at 25C is approximately +2.31 kJ. Since the enthalpy change is positive, the dissolution process is endothermic, meaning it absorbs heat from the surroundings.