Question

Calculate the enthalpy of solution for the dissolution of 15g of potassium chloride (KCl) in 100g of water (H2O) given that the temperature change was -12.5°C. The enthalpy of fusion for KCl is 17.2 kJ/mol and the specific heat capacity of water is 4.18 J/g•°C.

Answer 1

To calculate the enthalpy of solution, we first need to determine the moles of KCl and the heat absorbed by the water.1. Calculate the moles of KCl:KCl has a molar mass of 39.1 g/mol  K  + 35.45 g/mol  Cl  = 74.55 g/mol.moles of KCl = mass / molar massmoles of KCl = 15 g / 74.55 g/mol = 0.2012 mol2. Calculate the heat absorbed by the water:q = mcTwhere q is the heat absorbed, m is the mass of water, c is the specific heat capacity of water, and T is the temperature change.q =  100 g  4.18 J/gC  -12.5C  = -5225 JSince the temperature change is negative, the dissolution of KCl is exothermic, and the heat absorbed by the water is released by the KCl. Therefore, the heat released by KCl is 5225 J.3. Calculate the enthalpy of solution:Enthalpy of solution = heat released by KCl / moles of KClEnthalpy of solution = 5225 J / 0.2012 mol = 25975 J/molSince the dissolution is exothermic, the enthalpy of solution is negative:Enthalpy of solution = -25.975 kJ/mol