Question

Question #27862

Answer 1

`"4.5 moles Cl"_2`

Explanation:

You're dealing with a synthesis reaction in which aluminium metal, `"Al"`, reacts with chlorine gas, `"Cl"_2`, to form aluminium chloride, `"AlCl"_3`.

The balanced chemical equation that describes this reaction looks like this

`2"Al"_ ((s)) + color(red)(3)"Cl"_ (2(g)) -> color(blue)(2)"AlCl"_(3(s))`

Notice that you have a `color(red)(3):color(blue)(2)` mole ratio between chlorine gas and aluminium chloride. This tells you that for every `color(red)(3)` moles of chlorine gas that take part in the reaction, the reaction produces `color(blue)(2)` moles of aluminium chloride.

In other words, the reaction will consume `color(red)(3)/color(blue)(2)` times more moles of chlorine gas than the number of moles of aluminium chloride it will produce.

The problem tells you that the reaction produced `3` moles of aluminium chloride. This means that the reaction must have consumed

`3 color(red)(cancel(color(black)("moles AlCl"_3))) * (color(red)(3)color(white)(a)"moles Cl"_2)/(color(blue)(2)color(red)(cancel(color(black)("moles AlCl"_3)))) = color(green)(|bar(ul(color(white)(a/a)"4.5 moles Cl"_2color(white)(a/a)|)))`

As a conclusion, the stoichiometric coefficients listed in the balanced chemical equation can be used as mole ratios between the chemical species that take part in a given reaction.