Question

I have 3 Fe (s) + 4 (H2O) (g) reacts with FeO4 (s) + 4 H2 (g) How many g of steam and iron must react to produce 375 g of magnetic oxide Fe3O4 ? I need help trying to figure out how to write the equation please

Answer 1

How to write the equation? It's given to you but it would help if you wrote the product as Fe3O4 (which I suspect is a typo). Also, Fe and H2O don't react with Fe3O4 + H2. Fe and H2O yields Fe3O4 and H2.
3Fe(s) + 4H2O(g)==> Fe3O4(s) + 4H2(g)

Step 1. Write and balance the equation. I've made some minor adjustments to what you wrote.

Step 2. Convert grams of what you have to mols. mol = grams/molar mass = 375/molar mass Fe3O4 = ? mols Fe3O4

Step 3. Using the coefficients in the balanced equation, convert mols Fe3O4 to mols of what you want (in this case g steam and g Fe BUT you do these separately; i.e., that's two problems.)
To do that for Fe do ?mols Fe3O4 x (3 mols Fe/1 mol Fe3O4) = ? mols Fe3O4 x 3/1 = ?

Step 4. For the steam it's the same thing. ?mols Fe3O4 x (4 mols H2O/1 mol Fe3O4) = ? mols Fe3O4 x 4/1 = ?

Step 5. Now convert those mols Fe and mols H2O to grams.
g = mols x molar mass = ?

Answer 2

fe3o4 4h2 3fe 4h2o