Question

5g of hydrogen react with 32g of oxygen to form _ moles of water

Answer 1

2H2 +O2 ------ 2H2O

now 2 moles of hydrogen react with 1 mole of oxygen giving 2 moles of water
So first we remove the number of moles present in each reactant as there is a chance that any one of the reagent will be in excess amount or in limited amount(limiting reagent concept)
No. of Mole= given weight / molecular mass

No.of moles present in H =5/1=5moles

No. Of moles present in O= 32/32=1mole

So oxygen is the limiting reagent and the product will form accordingly.

Now in compound 1 mole if oxygen is forming 2moles of water
And the no. Of moles we calculated of oxygen is 1 thus 2 moles of water will be formed