Answer: -736.738 KJ/mol.
Explanation:
- The thermochemistrty that represents the reaction of iron with oxygen to produce rust and gives heat is:
4Fe + 3O₂ → 2Fe₂O₃, ΔH°f = -822.2 KJ/mol.
- The stichiometry of this reaction shows that 4 moles of Fe reacts with 3 moles of oxygen to give 2 moles of Fe₂O₃.
- Also, the formation of 1.0 mole of Fe₂O₃ gives -822.2 KJ/mol.
- Now, we need to know the number of moles of iron that will be in the reaction.
- n = mass / molar mass = 100.0 g / 55.8 g/mol = 1.79 mol.
- From the stichiometry of the reaction:
4.0 moles of Fe → 2.0 moles of Fe₂O₃
1.79 moles of Fe → ??? moles of Fe₂O₃
Using cross multiplication:
- The number of moles of Fe₂O₃ will produced from the reaction = (1.79 x 2.0) / (4.0) = 0.896 mole.
The production of 1.0 mole of Fe₂O₃ → -822.2 KJ/mol
The production of 0.896 mole of Fe₂O₃ → ???? KJ/mol
- The 100 g Fe will give = (-822.2 x 0.896) / (1.0) = -736.738 KJ/mol.
