Given the balanced equation representing a reaction:4Al(s) + 3O2(g) → 2Al2O3(s) + 3351 kJWhat is the number of moles of Al2O3(s) formed when 12 moles of O2(g) react completely?

Regents Chemistry Exam August 2025 Question 36

36 Given the balanced equation representing a reaction:

4Al(s) + 3O2(g) → 2Al2O3(s) + 3351 kJ

What is the number of moles of Al2O3(s) formed when 12 moles of O2(g) react completely?

(1) 8 mol

(2) 2 mol

(3) 3 mol

(4) 12 mol

Solution:

The coefficient in the balanced equation represent moles. There are 3 moles of O2 for 2 moles of Al2O3. If the number of moles of O2 increases to 12, which is four times more, the number of Al2O3 should be multiplied by four as well. We get 8 moles. Choice 1 is the correct answer.

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