Question

What is the mass of H2O produced when 10.0 grams of H2 react completely with 80.0 grams of O2

Answer 1

`2 \ H_2 + O_2 \to 2 \ H_2O`
2 moles of H₂ : 1 mole of O₂ : 2 moles of H₂O

number of moles of H₂ : number of moles of H₂O = 1 : 1


`m_(H_2)=10 \ g \\ M_(H_2)=2 \ (g)/(mol) \\ n_(H_2)=(10 \ g)/(2 (g)/(mol))=5 \ mol`

There are 5 moles of hydrogen so there must be 5 moles of water too.

`n_(H_2O)=5 \ mol \\ M_(H_2O)=18 \ (g)/(mol) \\ m_(H_2O)=5 \ mol * 18 \ (g)/(mol)=90 \ g`

The mass of H₂O is 90 g.