Question

Calculate the number of molecules of hydrogen that are required to completely react with 75.9L of oxygen at STP. The product of this reaction is water. Show all work including balanced equation.

Answer 1

2H₂ + O₂ = 2H₂O
n(O₂)=V/Vm, V-volume, Vm=22,4 dm³/mol at standard condition.
n(O₂)=75,9 dm³/22,4dm³/mol=3,39 mol
n(O₂):n(H₂)=1:2, n(H₂)=6,78 mol
N=n·Na(Avogadro number), N(H₂)=6,78 mol·6·²³ 1/mol = 40,68·10²³ molecules

Answer 2

 = 40,68·10²³ molecules

Hope this helps!