Question

What is the enthalpy change when dissolving 5 grams of NaOH in 100 ml of water at 25°C, given that the molar enthalpy of dissolution of NaOH is -44.5 kJ/mol?

Answer 1

To calculate the enthalpy change, 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 = mass / molar massNumber of moles = 5 g / 40 g/mol = 0.125 molNow, we can use the molar enthalpy of dissolution to find the enthalpy change:Enthalpy change = number of moles  molar enthalpy of dissolutionEnthalpy change = 0.125 mol   -44.5 kJ/mol  = -5.56 kJSo, the enthalpy change when dissolving 5 grams of NaOH in 100 ml of water at 25C is -5.56 kJ.