Answer:
3 mol Cl₂/2 mol AlCl₃ (three over two)
Step-by-step explanation:
Start with the balanced equation"
2Al + 3Cl₂⟶ 2AlCl₃
The steps in the calculation are
mass of AlCl₃ ⟶ moles of AlCl₃⟶ moles of Cl₂ ⟶ mass of Cl₂
The critical step is the conversion of moles.
You multiply the moles of AlCl₃ by a conversion factor to get moles of Al:
Moles of AlCl₃ × conversion factor = moles of Al.
The conversion factor is the molar ratio, and it uses the coefficients of the formulas in the balanced equation.
It is either (2 mol AlCl₃/3 mol Cl₂) or (3 mol Cl₂/2 mol AlCl₃).
You choose the one that has the desired units of the answer in the numerator.
We choose the second option, because it has the correct units.
For example,
[tex]\text{0.2 mol AlCl}_{3} \times \frac{3\textbf{ mol Cl}_{2} }{ 2\text{ mol AlCl}_{3} } = 0.3\textbf{ mol Cl}_{2})[/tex]
Notice how the units "mol AlCl₃" cancel and the correct units appear in the answer.
If we had used the other conversion factor, we would have gotten the wrong units.
