Kat A.

asked • 05/16/15# For the reaction : 4Fe+3O2-->2Fe2O3, if 100 g of Fe are used how much Fe2O3 are produced?

I'm having such a hard time with this..It's my physics HW and I don't know how to solve this.

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## 1 Expert Answer

Stephanie M. answered • 05/16/15

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Ian's answer is correct. I just want to expand on why he did what he did.

We'd first like to figure out

*how many moles of Fe 100 grams is*.You can figure that out by looking at Fe's atomic mass on the Periodic Table: 55.85. That tells you that 1 mole of Fe weighs 55.85 grams.

**There are 55.85 g/mol of Fe, or 1 mol of Fe/55.85 g**. Use the latter to convert 100 g into mol, since that way the units will work out:100 g × 1 mol / 55.85 g = 100 g×mol / 55.85 g = 100 mol / 55.85 = 1.79 mol

Now, let's figure out

*how many moles of Fe*, since there are 1.79 moles of Fe. The reaction equation tells you that 4 moles of Fe and 3 moles of O_{2}O_{3}there are_{2}will produce 2 moles of Fe_{2}O_{3}. The relevant part of that for us is that 4 moles of Fe will produce 2 moles of Fe_{2}O_{3}. In other words,**there are 4 mol Fe/2 mol Fe**. Use the latter to convert to moles of Fe_{2}O_{3}, or 2 mol Fe_{2}O_{3}/4 mol Fe_{2}O_{3}, since that way the units will work out:1.79 mol Fe × 2 mol Fe

_{2}O_{3}/ 4 mol Fe = (1.79(2) mol Fe × mol Fe_{2}O_{3}) / 4 mol Fe = 3.58 mol Fe_{2}O_{3}/ 4 = 0.895 mol Fe_{2}O_{3}Finally, let's figure out

*how many grams of Fe*if we have 0.895 moles. First, we'll need to use the atomic masses of Fe and O to find out how many moles there are per gram. We've got 2 Fe molecules and 3 O molecules, so we'll just find the atomic mass of Fe and multiply it by 2, then add that to the atomic mass of O multiplied by 3:_{2}O_{3}there are2(55.85 g/mol of Fe) + 3(16.00 g/mol of O) = 111.7 + 48.00 g/mol of Fe2O3 = 159.7 g/mol of Fe

_{2}O_{3}So,

**there are 159.7 g/mol of Fe**. Use the former to convert 0.895 mol of Fe_{2}O_{3}, or 1 mol of Fe_{2}O_{3}/159.7 g_{2}O_{3}into g, since that way the units will work out:0.895 mol × 159.7 g / mol = 0.895(159.7) mol×g / mol = 142.9315 g

Thus,

**142.93 grams of Fe**._{2}O_{3}are producedSo, just to review, the steps were:

1. Figure out how many moles of Fe there are, given 100 grams of Fe

2. Figure out how many moles of Fe

_{2}O_{3}there are, given 1.79 moles of Fe3. Figure out how many grams of Fe

_{2}O_{3}there are, given 0.895 moles of Fe_{2}O_{3}That's exactly what Ian did; he just did it all in one step (and I think he made a slight error in multiplication, which is why his answer is a couple grams off):

100 g Fe x (1 mol Fe / 55.85 g Fe) x (2 mol Fe

_{2}O_{3}/ 4 mol Fe) x (159.69 g Fe_{2}O_{3}/ mol Fe_{2}O_{3})100 g Fe x (conversion to mol Fe) x (conversion to mol Fe

_{2}O_{3}) x (conversion to g Fe_{2}O_{3})Stephanie M.

tutor

Also, as a side note, if you were given this in your physics class, no wonder you're confused... This is unquestionably a

*chemistry*problem, not physics!
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05/16/15

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Ian D.

05/16/15