In the chemical reaction 2H₂ + O2 → 2H₂O, two moles of hydrogen react with one mole of oxygen to produce two moles of water. If you have 3.31 moles of hydrogen, you need 3.31/2 = 1.655 moles of oxygen to react with it.
To find the number of grams of oxygen needed, we can use the molar mass of oxygen, which is 16 grams/mole. The number of grams of oxygen needed is given by the formula:
grams of oxygen = moles of oxygen * molar mass of oxygen
Substituting the values and solving, we find that:
grams of oxygen = 1.655 moles * 16 grams/mole
= 26.88 grams
Therefore, you need 26.88 grams of oxygen to react with 3.31 moles of hydrogen in the given chemical reaction.