Calculating Oxygen Reacted in Chemical Reaction

If you burn 50.4 g of hydrogen and produce 4.50 × 10² g of water, how much oxygen reacted?

moles H2O = 362 / 18.02 g/mol = 20

2 H2 + O2 = 2 H2O

moles H2 = 40.5 g / 2.016 g/mol = 20

the ratio between H2 and H2O is 2 : 2 so the yield is 100%

moles O2 required = 20 / 2 = 10

mass O2 = 10 mol x 32 g/mol = 320 g

Reaction involved: 2H₂ + O₂ → 2H₂O

In this reaction, 2 moles (2 g/mol) of H₂ reacts with 1 mole (32 g/mol) of O₂ to give 2 moles of H₂O (18 g/mol).

Given: 50.4 g H₂ reacts to give 4.50 × 10² g water.

Number of moles of H₂ burned = 50.4 g ÷ 2 g/mol = 25.2 moles

Number of moles of H₂O formed = 4.50 × 10² g ÷ 18 g/mol = 25 moles

∵ 2 moles H₂O is formed from 1 mole O₂

∴ The number of moles of O₂ that reacts to give 25 moles H₂O = 25 moles ÷ 2 moles = 12.5 moles

Therefore, the amount of O₂ reacted to give 4.50 × 10² g H₂O = 12.5 mole × 32 g/mol = 400 g