Problem:

Using the reaction:

2 H₂ + O₂ ==> 2 H₂O

Determine how many mol O₂ are needed to react with 36 mol H₂.

Step 1: Write what you are given.



Step 2: Pick the correct mole ratio conversion factor.
Since "H₂" and "O₂" are both in the problem, it should contain both "H₂" and "O₂" in the conversion factor. Choose the one with "mol H₂" on the bottom to cancel out the "mol H₂" on the top.



Step 3: Cancel the units.


Step 4: Do the math.


The answer should be reported as 18 mol O₂.

There are 2 sig figs in the given (36 mol H₂), therefore the answer should also have 2 sig figs.