If a mole of hydrogen reacts with a mole of oxygen to produce water, what is the excess reactant?

Answer 1

Looking at the balance equation for the production of water (H₂O), we have...

2H₂ + O₂ ==> 2H₂O

From this, you can see that 2 moles H₂ react with 1 mole of O₂ to produce 2 moles of H₂O.

If 1 mole of H₂ reacts with 1 mole of O₂, the excess react would therefore have to be O₂.

Looking at it another way:

1 mole H₂ x 2 moles H₂O/2 moles H₂ = 1 mole H₂O can be produced from 1 mole H₂

1 mole O₂ x 2 moles H₂O/1 mole O₂ = 2 moles H₂O can be produced from 1 moles O₂

Since you can make more water from the oxygen, the hydrogen is limiting and the oxygen is in excess