[grfeathers]

What mass of iron oxide is produced by the complete oxidation of 100g of iron according to the equation 4Fe +3O2 --> 2Fe2O3?

(The 2 after the first O and the second Fe and the 3 after the last O are supposed to be small but I don't know how to do that on this keyboard)

[Arkcon]

Greetings !!! And welcome to the board!!! Oxidation!!! Who-hoo!!!

Ahem ..

You've been given a mass of reactant, and you need a mass of product.  You will have to convert one to the other.  You will need a conversion equation, and you have one, the balanced chemical equation.  It has units, it just doesn't include the symbols.  Can you figure out what to convert, and where.

P.S. give the _sub button up above a try when you next need to make subscripts.

[grfeathers]

I have no idea what to do first! :-(

[Arkcon]

Well, the word oxidation doesn't mean much, in this case, so I hope you can clear your mind of that.  This is a pretty early type of chemistry class problem, so you may be able to find a step by step similar problem in your class notes or textbook.  Can you take a stab at the problem in a general way?  Will the mass be more or less?  Why?  And by how much -- in a general sort of way?  And what will you need to know to find out exactly how much?  See if those hints pull the work together for you.