How many grams of water can be made from 64 g of oxygen water

Question

From the equation: 2H2 + O2 —-> 2H2O

Answer 1

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

Assuming that H₂ is present in excess, we can determine moles of O₂ present, and then moles and grams of H₂O produced.

moles O₂ present = 64 g O₂ x 1 mole O₂/32 g O₂ = 2 moles O₂ present

moles H₂O produced = 2 moles O₂ x 2 mole H₂O / 1 mole O₂ = 4 moles H₂O produced

grams of H₂O produced = 4 moles H₂O x 18 g H₂O/mole H₂O = 72 g H₂O produced

Answer 2

Using the molar mass value for oxygen, find the number of moles of oxygen

64 g O₂ / (32 g O₂ / mol O₂) = 2 mol O₂

and use stoichiometry to convert to the number of moles of water.

2 mol O₂ * (2 mol H₂O/ 1 mol O₂) = 4 mol H₂O

Then convert number of moles of water to grams using the molar mass of water.

4 mol H₂O * (18 g H₂O/ mol H₂O) = 72 g H₂O