Hydrochloric acid reacts with calcium to form hydrogen and calcium chloride. If 100 grams of hydrochloric acid reacts with 100 grams of calcium, what is the limiting reactant?
2HCl + Ca --> CaCl2 + H2
To determine the limiting reactant, we need to compare the amounts of hydrochloric acid (HCl) and calcium (Ca) to see which one will be completely consumed in the reaction.
1. Calculate the number of moles for each substance:
- Hydrochloric acid (HCl):
The molar mass of HCl is 1 gram/mole (1 H + 35.5 Cl). Therefore, 100 grams of HCl is equal to 100 moles.
- Calcium (Ca):
The molar mass of Ca is 40 grams/mole. Therefore, 100 grams of Ca is equal to 2.5 moles.
2. Write out the balanced chemical equation for the reaction:
2HCl + Ca --> CaCl2 + H2
3. Compare the stoichiometric ratio of HCl to Ca:
From the balanced equation, we see that 2 moles of HCl react with 1 mole of Ca. This means that the stoichiometric ratio is 2:1, HCl:Ca.
4. Determine the limiting reactant:
To find the limiting reactant, we need to compare the actual ratio of HCl to Ca to the stoichiometric ratio.
From step 1, we have:
- HCl: 100 moles
- Ca: 2.5 moles
Divide both quantities by the stoichiometric coefficients:
- HCl: 100 moles / 2 = 50 moles
- Ca: 2.5 moles / 1 = 2.5 moles
Since the actual ratio of HCl to Ca is 50:2.5, it is clear that calcium (Ca) is the limiting reactant because it is present in a smaller quantity compared to the stoichiometric ratio.
Therefore, calcium (Ca) is the limiting reactant in this reaction.
To determine the limiting reactant, we need to compare the number of moles of each reactant available and see which one is present in fewer moles compared to the stoichiometric ratio.
First, we need to convert the mass of each reactant to moles using their respective molar masses. The molar mass of hydrochloric acid (HCl) is 36.46 g/mol, and the molar mass of calcium (Ca) is 40.08 g/mol.
Moles of HCl = mass of HCl / molar mass of HCl
Moles of HCl = 100 g / 36.46 g/mol
Moles of HCl ≈ 2.74 mol
Moles of Ca = mass of Ca / molar mass of Ca
Moles of Ca = 100 g / 40.08 g/mol
Moles of Ca ≈ 2.50 mol
By comparing the number of moles, we see that there are fewer moles of calcium (2.50 mol) compared to hydrochloric acid (2.74 mol). Therefore, calcium is the limiting reactant in this reaction.
This is a limiting reagent problem. Here is a worked example that will take care of all of your limiting reagent problems.
http://www.jiskha.com/science/chemistry/limiting_reagent_problem.html