i need help with chemstry?

Question

i need help on this problem,
Hydrogen gas wa perpared in 1776 by Cavendish by passing steam through a red-hot iron rifle barrel, this process also produced Fe3O4. What mass of iron react in the production of 73.6dm3 of hydrogen measured at STP?

Answer 1

First write out a balanced equation.

8H2O (g) + 6Fe (s) -> 2HFe3O4 (s) + 7H2 (g)

1 dm^3 is equal to 1 liter
22.4 Liters per mol at STP for ideal gas

So 73.6 L H2 / 22.4 L H2 * 6 mol Fe / 7 mol H2 * 55.85 g Fe/ mol Fe = 157 g Fe

Hopefully that makes sense.

Answer 2

We know how much H2 is produced, since 1 mole of H2 at STP occupies 22.4 dm^3 of volume. For arguement sake, call it 3.3 moles.

The reaction of interest is
3 Fe + 4H2O --> Fe3O4 + 4H2
This tells us that 4 moles of H2 require 3 g-atoms of Fe. So we can set up a proportion
[ 3 / 4 ] the reaction = [ x / 3.3 ]the process
x = 2.5 g-atoms of iron or so.
I believe Fe is about 56 atomic weight, so the answer should be about 140 grams.