# Homework Help: How much MgO is formed when 10 kg of Mg reacts with 10 kg kg of O2

1. Sep 22, 2009

### Zhalfirin88

1. The problem statement, all variables and given/known data
How much MgO is formed when 10 kg of Mg reacts with 10 kg kg of O2

3. The attempt at a solution

The balanced equation is:

2Mg + O2 $$\rightarrow$$ 2MgO

What do I do next? Do I find how many grams of MgO is produced by 10 kg of Mg and add it to the amount of grams that is produced by 10 kg of O2?

2. Sep 22, 2009

### Ygggdrasil

Re: Reactants

First, you should find out the number of moles of Mg and O2 that you start with. Next, you need to figure out which is the limiting reagent (i.e. which reactant runs out first). For example, if you start with 4 moles of Mg and 4 moles of O2, you can only make 4 moles of MgO because you run out of Mg before you use up all of the oxygen.

3. Sep 22, 2009

### Zhalfirin88

Re: Reactants

How did you know it's a limiting reagents problem?

4. Sep 22, 2009

### Bohrok

Re: Reactants

Because 10kg of Mg and 10kg of O2 will not produce the same amount of MgO in that reaction; 2 mol Mg and 1 mol O2 dont' have the same weight.

5. Sep 22, 2009

### Ygggdrasil

Re: Reactants

Whenever you need to figure out the yield of a reaction, you will always need to figure out which reagent is limiting unless 1) there is only 1 reactant or 2) they tell you which reactant is limiting (or which reactants are in excess).