Question

Calculate the standard enthalpy change for the dissolution of 5.00 g of solid sodium hydroxide (NaOH) in water, given that the molar enthalpy of dissolution of NaOH is -44.51 kJ/mol. Assume that the specific heat capacity and density of the solution are the same as pure water and that no heat is lost to the surroundings during the dissolution process.

Answer 1

To calculate the standard enthalpy change for the dissolution of 5.00 g of solid sodium hydroxide  NaOH  in water, we first need to determine the number of moles of NaOH being dissolved. The molar mass of NaOH is:Na = 22.99 g/molO = 16.00 g/molH = 1.01 g/molTotal = 22.99 + 16.00 + 1.01 = 40.00 g/molNow, we can find the number of moles of NaOH in 5.00 g:moles = mass / molar massmoles = 5.00 g / 40.00 g/mol = 0.125 molNext, we can use the molar enthalpy of dissolution to find the standard enthalpy change for the dissolution of 5.00 g of NaOH:H = moles  molar enthalpy of dissolutionH = 0.125 mol   -44.51 kJ/mol  = -5.56 kJThe standard enthalpy change for the dissolution of 5.00 g of solid sodium hydroxide in water is -5.56 kJ.