Question

Calculate the enthalpy change for the dissolution of 10 grams of sodium hydroxide in excess water, given that the solution formed has a final temperature of 25°C, and the specific heat capacity of the solution is 4.184 J/(g°C). The molar enthalpy of dissolution of NaOH is -44 kJ/mol. Assume that the density of the solution is equal to that of water.

Answer 1

To calculate the enthalpy change for the dissolution of 10 grams of sodium hydroxide in excess water, we first need to determine the number of moles of NaOH being dissolved. The molar mass of NaOH is approximately 40 g/mol  23 g/mol for Na, 16 g/mol for O, and 1 g/mol for H .Number of moles of NaOH =  mass of NaOH  /  molar mass of NaOH Number of moles of NaOH =  10 g  /  40 g/mol  = 0.25 molNow, we can use the molar enthalpy of dissolution of NaOH  -44 kJ/mol  to calculate the total enthalpy change for the dissolution of 0.25 mol of NaOH.Enthalpy change =  number of moles of NaOH    molar enthalpy of dissolution of NaOH Enthalpy change =  0.25 mol    -44 kJ/mol  = -11 kJThe enthalpy change for the dissolution of 10 grams of sodium hydroxide in excess water is -11 kJ.