Question

Calculate the enthalpy change of dissolving 10 grams of NaCl in 100 mL of water, assuming the resultant solution has a density of 1.0 g/mL and assuming that the heat evolved is absorbed by the water. Given: the enthalpy of hydration of NaCl is -787 kJ/mol.

Answer 1

To calculate the enthalpy change of dissolving 10 grams of NaCl in 100 mL of water, we need to determine the number of moles of NaCl and then use the enthalpy of hydration to find the total enthalpy change.First, let's find the number of moles of NaCl:NaCl has a molar mass of 58.44 g/mol  22.99 g/mol for Na and 35.45 g/mol for Cl .moles of NaCl = mass / molar massmoles of NaCl = 10 g / 58.44 g/molmoles of NaCl  0.171 molNow, we can use the enthalpy of hydration to find the enthalpy change:Enthalpy change = moles of NaCl  enthalpy of hydrationEnthalpy change = 0.171 mol   -787 kJ/mol Enthalpy change  -134.6 kJThe enthalpy change of dissolving 10 grams of NaCl in 100 mL of water is approximately -134.6 kJ.