Question

How many kilojoules are required to produce 1.83 mol of aluminum? How many kilocalories are required to produce 10.9 g of aluminum?

Answer 1

When aluminum oxide (Al₂O₃) is heated at high temperatures, it decomposes to aluminum metal by the following thermochemical equation:

2Al₂O₃(s) ----->4Al(s) + 3O₂ (g)   ΔH° = +3350 kJ

As per stoichiometric equation,

To produce 4 moles of aluminum, 3350 kJ of energy is required

So, to produce 1.83 mol of Al, energy required = 1.83 mol Al x (3350 kJ/4 mol Al)

         = 1532.63 kJ

To calculate kilocalories are required to produce 10.9 g of aluminum, first convert +3350 kJ to kcal

  4.182 kJ = 1 kcal

So, 3350 kJ = 3350 kJ x (1 kcal/4.182 kJ) = 801.05 kcal

Molar mass of Al = 26.982 g/mol

Convert 10.9 g Al to moles of Al by dividing with its molar mass

Moles of Al = 10.9g/26.982 g/mol = (10.9/26.982) moles

To produce 4 moles of aluminum, 801.05 kcal of energy is required

So, to produce (10.9/26.982) mol of Al, energy req = (10.9/26.982 moles) mol Al x (801.05kcal/4 mol Al)

                                                                        = 80.90 kcal