Question

What is the enthalpy change, in kilojoules per mole, when 6.0 grams of potassium chloride (KCl) is dissolved in 200.0 mL of water at 25°C? The molar heat of dissolution of KCl is -57.3 kJ/mol.

Answer 1

To calculate the enthalpy change, we first need to determine the number of moles of KCl being dissolved. The molar mass of KCl is:K = 39.1 g/molCl = 35.5 g/molKCl = 39.1 + 35.5 = 74.6 g/molNow we can find the number of moles of KCl:moles = mass / molar massmoles = 6.0 g / 74.6 g/mol = 0.0804 molNext, we can use the molar heat of dissolution to find the enthalpy change:enthalpy change = moles  molar heat of dissolutionenthalpy change = 0.0804 mol   -57.3 kJ/mol  = -4.61 kJThe enthalpy change when 6.0 grams of potassium chloride is dissolved in 200.0 mL of water at 25C is -4.61 kJ.