30g of hydrogen is mixed with 100g of oxygen.
The balanced equation is 2H2 +O2 = 2H2O.
Determine the limiting reagents and excess reagents.
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.
To determine the limiting and excess reagents, we need to compare the number of moles of each reactant to the stoichiometric ratio in the balanced equation.
Let's calculate the number of moles for hydrogen and oxygen:
1. Hydrogen:
Given: Mass of hydrogen = 30g
Molar mass of hydrogen (H2) = 2g/mol
Number of moles = Mass / Molar mass
Number of moles of hydrogen = 30g / 2g/mol = 15 mol
2. Oxygen:
Given: Mass of oxygen = 100g
Molar mass of oxygen (O2) = 32g/mol
Number of moles = Mass / Molar mass
Number of moles of oxygen = 100g / 32g/mol = 3.125 mol
Now, let's compare the number of moles of hydrogen and oxygen to the stoichiometric ratio in the balanced equation:
From the balanced equation: 2H2 + O2 = 2H2O
The stoichiometric ratio of hydrogen to oxygen is 2:1.
- The number of moles of hydrogen is 15 mol, and according to the stoichiometric ratio, it should react with half the moles of oxygen (7.5 mol).
- The number of moles of oxygen is 3.125 mol, but according to the stoichiometric ratio, it should react with twice the moles of hydrogen (6.25 mol).
Now let's compare the moles experimentally available with the calculated stoichiometric ratios:
Hydrogen (H2):
Available: 15 mol
Required: 7.5 mol (stoichiometric ratio requirement)
Oxygen (O2):
Available: 3.125 mol
Required: 6.25 mol (stoichiometric ratio requirement)
From the comparison, we can see that the number of moles of oxygen (3.125 mol) is less than its stoichiometric requirement (6.25 mol). Therefore, oxygen is the limiting reagent.
The hydrogen (H2) is in excess because the available moles (15 mol) are greater than its stoichiometric requirement (7.5 mol).
To summarize:
- Limiting reagent: Oxygen (O2)
- Excess reagent: Hydrogen (H2)