If you burn 55.6 g of hydrogen and produce 497 g of water, how much oxygen reacted?

Answer 1

Actually, the very first thing you need to do is to write the correctly balanced equation so that you can see what the mole ratios are between hydrogen, oxygen and water.

2H₂ + O₂ ==> 2H₂O ... balanced equation

NOTE the mol ratio between H₂ and O₂ is 2:1 and between H₂ and H₂O is 1:1

Using dimensional analysis and converting to moles we have...

497 g H₂O x 1 mol H₂O/18 g x 2 mol H₂/2 mol H₂O x 1 mol O₂/2 mol H₂ = 13.8 moles O₂ (answer in moles)

If you want mass of O2 reacted, convert as follows:

13.8 mol O₂ x 32 g O₂/mol O₂ = 442 g O₂

Answer 2

Remember, for a question like this first convert mass to mole to find the ratio of the components. Then, covert back to mass to find how much of a component is used.