Question

Calculate the enthalpy of solution for dissolving 5 grams of NaCl in 100 mL of water if the final temperature of the solution is 25°C and the initial temperature of the water was 20°C. The enthalpy of fusion of NaCl is -3.0 kJ/mol and the specific heat capacity of the solution is 4.18 J/g°C.

Answer 1

To calculate the enthalpy of solution for dissolving 5 grams of NaCl in 100 mL of water, we need to consider the heat absorbed by the water and the heat released by the NaCl.First, let's find the moles of NaCl:NaCl has a molar mass of 58.44 g/mol.moles of NaCl = mass / molar massmoles of NaCl = 5 g / 58.44 g/mol = 0.0856 molNow, let's find the heat absorbed by the water:q_water = mass_water * specific heat capacity * change in temperaturemass_water = 100 g  assuming the density of water is 1 g/mL change in temperature = final temperature - initial temperature = 25C - 20C = 5Cq_water = 100 g * 4.18 J/gC * 5C = 2090 JNext, let's find the heat released by the NaCl:q_NaCl = moles of NaCl * enthalpy of fusionq_NaCl = 0.0856 mol * -3.0 kJ/mol * 1000 J/kJ = -256.8 JNow, we can find the enthalpy of solution:q_solution = q_water + q_NaClq_solution = 2090 J +  -256.8 J  = 1833.2 JFinally, we can find the molar enthalpy of solution by dividing the enthalpy of solution by the moles of NaCl:molar enthalpy of solution = q_solution / moles of NaClmolar enthalpy of solution = 1833.2 J / 0.0856 mol = 21416.3 J/molThe enthalpy of solution for dissolving 5 grams of NaCl in 100 mL of water is 21416.3 J/mol.