# In the reaction H_2S + 2O_2 -> H_2SO_4, the law of definite proportions predicts that for every mole of H_2S, you will need how many moles of O_2?

What is the relationship between molecules and moles? A mole is simply Avogadro's number of molecules, a very large number, i.e. ${N}_{A} = 6.022 \times {10}^{23}$ $m o {l}^{-} 1$. In the reaction you have given above, I could CORRECTLY say that 1 molecule of hydrogen sulfide reacts, or 1 MOLE of hydrogen sulfide reacts.