Vocabulary
The reactant that gets used up first.
Limiting reagent
2H₂ + O₂ → 2H₂O
Start with 6 H₂ particles and 4 O₂ particles.
H₂
2H₂ + O₂ → 2H₂O
Start with 8 H₂ particles and 5 O₂ particles.
What is the maximum number of H₂O particles you can form?
8 H₂O particles
2H₂ + O₂ → 2H₂O
What is the ratio of H₂ to O₂?
2 : 1
True or False: The reactant you have less of is always limiting.
False: The limiting reagent depends on the stoichiometric ratio in the reaction, not just which reactant has a smaller amount. You could have less of a reactant but still have excess if the ratio requires even less of it.
The reactant left over after the reaction stops.
Excess reactant.
N₂ + 3H₂ → 2NH₃
Start with 2.0 mol H₂ and 1.0 mol N₂.
H₂
N₂ + 3H₂ → 2NH₃
Start with 2.0 mol H₂ and 1.0 mol N₂.
What is the maximum moles of NH₃ produced?
1.33 mol NH₃
4Li + O₂ → 2Li₂O
What is the ratio of Li : O₂ in this reaction?
4 : 1
If O₂ is limiting, adding more H₂ will increase products.
False. The reaction can only produce as much product as the limiting reagent allows. Adding more H₂ won’t help because O₂ will still run out first.
What stops when the limiting reagent is used up?
The reaction/making of product
Al + 3Cl₂ → 2AlCl₃
Start with 10.0 g Al and 40.0 g Cl₂.
Al
2Al + 3Cl₂ → 2AlCl₃
Start with 10.0 g of Al and 40.0 g of Cl₂.
How many grams of AlCl₃ can be produced?
49.4 g AlCl₃
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
What is the ratio of C₃H₈ : O₂?
1 : 5
If both reactants run out at the same time, which is limiting?
None- If both are completely used up together, the reactants are in the exact stoichiometric ratio, so there is no limiting reagent.
The branch of chemistry that studies the quantitative relationships between the reactants and products of a balanced chemical reaction.
Stoichiometry.
4Li + O₂ → 2Li₂O
Start with 3.0 × 10²² Li atoms and 0.50 mol O₂.
Li
4Li + O₂ → 2Li₂O
Start with 3.0 × 10²² Li atoms and 0.50 mol O₂.
Maximum moles of Li₂O produced?
0.025 mol Li₂O
2Al + 3Cl₂ → 2AlCl₃
What is the ratio of Al : Cl₂ AND Cl₂ : AlCl₃?
Al : Cl₂ = 2 : 3
Cl₂ : AlCl₃ = 3 : 2
Can the excess reagent be fully consumed without changing the recipe?
No. You would have to add more limiting substance to use up the excces
A chemical recipe using coefficients.
Balanced chemical equation.
2K + Br₂ → 2KBr
Start with 15.0 g K and 30.0 g Br₂.
K
2K + Br₂ → 2KBr
Start with 15.0 g K and 30.0 g Br₂
What is the mass of KBr produced?
45.7 g KBr
6Fe + 4O₂ → 2Fe₃O₄
What is the ratio of Fe : O₂ : Fe₃O₄?
3 : 2 : 1 (simplified)
The reactant that has the smaller coefficient in the balanced equation is always the limiting reagent.
False. The coefficient has nothing to do with which reactant is limiting — it depends on the amount you start with, not the coefficient size.