30g of hydrogen is mixed with 100g of oxygen.

Question

The balanced equation is 2H2 +O2 = 2H2O.
Determine the limiting reagents and excess reagents.

Answer 1

I work these limiting reagent (LR) problems the long way.
1. How many mols H2 do you have? mols = grams/molar mass = 30/2 15
1a. How much H2O COULD THIS FORM? That's
15 mols H2 x (2 mols H2O/2 mols H2) = 15 mols H2O IF WE HAD ALL OF THE OXYGEN NEEDED.

2. How many mols O2 do we have? That's 10032 = approx 3 but that's just an estimate. You need to redo all of these calculatons.
2a. How much H2O COULD BE FORMED? That's
3 mols O2 x (2 mols H2O/1 mol O2 = approx 6 IF WE HAD ALL OF THE HYDROGEN WE NEEDED.

Now compare mols H2O that could be formed in 1a and 2a. Oxygen is the LR because that's the smaller number. So O2 is the LR and H2 is the excess reagent.