What is the limiting reactant when 31.5 g of
CuO are exposed to 2.7 g of H2 according to
the equation
CuO(s) + H2(g) −→ Cu(s) + H2O(g) ?
1. Neither is limiting.
2. Unable to determine.
3. CuO
4. H
#3 is the answer, CuO is the limiting reactant
Convert 2.7 g H2 to moles. moles = grams/molar mass
Convert 31.5 g CuO to moles the same way.
Using the coefficients in the balanced equation, convert moles H2 to moles Cu.
Do the same for CuO to moles Cu. You will obtain two answers and only one can be right; the correct one in limiting reagent problems is ALWAYS the smaller one and the reagent providing that number is the limiting reagent.
To determine the limiting reactant, we need to compare the amounts of each reactant to the stoichiometric ratio in the balanced equation.
The balanced equation is:
CuO(s) + H2(g) → Cu(s) + H2O(g)
The molar mass of CuO is 79.55 g/mol, and the molar mass of H2 is 2.02 g/mol.
To find the moles of CuO, we divide the mass by the molar mass:
moles of CuO = 31.5 g / 79.55 g/mol = 0.396 mol
To find the moles of H2, we divide the mass by the molar mass:
moles of H2 = 2.7 g / 2.02 g/mol = 1.34 mol
Now we can compare the ratio of moles of CuO to H2 in the balanced equation:
1 mol CuO : 1 mol H2
0.396 mol CuO : 1.34 mol H2
From the ratio above, it is clear that the amount of H2 is in excess compared to CuO. Therefore, the limiting reactant is CuO.
The correct answer is: 3. CuO
To determine the limiting reactant in a chemical reaction, you need to compare the amount of each reactant to their respective stoichiometric coefficients. The reactant that is present in the least amount compared to the stoichiometry is the limiting reactant.
To find the limiting reactant, follow these steps:
Step 1: Convert the given masses of CuO and H2 to moles.
The molar mass of CuO is 63.55 g/mol, and the molar mass of H2 is 2.016 g/mol.
Moles of CuO = mass / molar mass = 31.5 g / 63.55 g/mol = 0.495 mol
Moles of H2 = mass / molar mass = 2.7 g / 2.016 g/mol = 1.34 mol
Step 2: Write and balance the equation for the reaction.
CuO(s) + H2(g) → Cu(s) + H2O(g)
Step 3: Compare the moles of each reactant to the stoichiometric coefficients in the balanced equation to determine the limiting reactant.
From the balanced equation, you can see that the stoichiometric coefficient for CuO is 1, and for H2 is 1. Therefore, the ratio of CuO to H2 required to react completely is 1:1.
Since the moles of CuO (0.495 mol) and H2 (1.34 mol) are in a 1:1 ratio, H2 is in excess, and CuO is the limiting reactant.
Therefore, the answer is option 3: CuO is the limiting reactant.