Question #1b172

Question

3002 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2015-10-05T00:32:56

You need $color(blue)("5.86 mol of O"""_2)$ .

Your balanced equation is

$"4Fe" + "3O"_2 → "2Fe"_2"O"_3$

This tells you that $"2 mol of Fe"""_2"O"_3$ require $"3 mol of O"""_2$ .

This is called the molar ratio of $"Fe"_2"O"_3$ to $"O"_2$ .

You want to convert the given moles of $"Fe"_2"O"_3$ to moles of $"O"_2$ .

We can use the molar ratio to create a conversion factor.

It will be either $("2 mol Fe"""_2"O"_3)/("3 mol O"""_2)$ or $("3 mol O"""_2)/("2 mol Fe"""_2"O"_3)$ .

We choose the one that will give us the correct units in the answer.

It will be the second one. Then

$3.91 color(red)(cancel(color(black)("mol Fe"_2"O"_3))) × ("3 mol O"""_2)/(2 color(red)(cancel(color(black)("mol Fe"_2"O"_3)))) = "5.86 mol O"""_2$

Notice that the units cancelled to give the desired units of $"mol O"""_2"$ .

If we had chosen the other conversion factor, we would not have gotten the correct units.