Question #1b172

1 Answer

Answer:

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

Explanation:

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.