1. Write the balanced chemical equation:

2 Al + 3 Cl₂ → 2 AlCl₃

This equation tells us that 2 moles of aluminum (Al) react with 3 moles of chlorine gas (Cl₂) to produce 2 moles of aluminum chloride (AlCl₃).

2. Determine the mole ratio:

The balanced equation shows a 2:2 mole ratio between aluminum and aluminum chloride. This means that for every 2 moles of aluminum that react, 2 moles of aluminum chloride are produced.

3. Calculate the moles of aluminum chloride:

Since we have 4 moles of aluminum, and the mole ratio is 2:2, we can set up a proportion:

(2 moles AlCl₃ / 2 moles Al) = (x moles AlCl₃ / 4 moles Al)

Solving for x, we get:

x = 4 moles AlCl₃

Answer: When 4 moles of aluminum react with excess chlorine gas, 4 moles of aluminum chloride are produced.