Balancing Acts
Balance: ___ H₂ + ___ O₂ → ___ H₂O
2H₂ + O₂ → 2H₂O
What is a mole ratio?
A ratio between coefficients in a balanced equation.
What is a limiting reactant?
The reactant that runs out first and limits product formation.
Define Theoretical Yield
The max amount of product predicted by stoichiometry.
What’s the mole ratio between Fe and O₂ in 4Fe + 3O₂ → 2Fe₂O₃?
4:3
Balance: ___ N₂ + ___ H₂ → ___ NH₃
N₂ + 3H₂ → 2NH₃
From: 2H₂ + O₂ → 2H₂O, what’s the mole ratio between H₂ and H₂O?
2:2 or 1:1
What happens to excess reactant?
It's left over after the reaction finishes.
(Actual yield ÷ Theoretical yield) × 100
What’s conserved in a chemical reaction?
Mass and Atoms
Balance: ___ Fe + ___ O₂ → ___ Fe₂O₃
4Fe + 3O₂ → 2Fe₂O₃
From: N₂ + 3H₂ → 2NH₃, how many moles of H₂ react with 4 moles of N₂?
12 moles of H₂
In 2H₂ + O₂ → 2H₂O, if you have 5 mol H₂ and 2 mol O₂, which is limiting?
O₂ is limiting.
If theoretical yield = 10 g and actual = 8 g, percent yield = ?
80%
2Na + Cl₂ → 2NaCl. If you start with 3 mol Na, how many mol NaCl form?
3 mol NaCl
Why must equations be balanced before using stoichiometry?
To conserve mass, the law of conservation of matter.
In 2Al + 3Cl₂ → 2AlCl₃, how many moles of AlCl₃ are made from 9 moles of Cl₂?
6 moles AlCl₃
Why is identifying the limiting reactant important?
It determines the maximum product yield.v
Why can percent yield be less than 100%?
Product lost, incomplete reaction, or measurement error.
2H₂O → 2H₂ + O₂. How many grams of O₂ from 36 g H₂O?
36 g H₂O × (1 mol/18 g) × (1 mol O₂/2 mol H₂O) × (32 g/mol) = 32 g O₂
Balance: ___ C₃H₈ + ___ O₂ → ___ CO₂ + ___ H₂O
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
Explain how to use mole ratios in stoichiometry.
Use balanced coefficients to convert between substances.
A reaction needs 3 mol Cl₂ per 2 mol Al. If you have 4 mol Al and 4 mol Cl₂, which limits?
Cl₂ limits (needs 6 mol for 4 mol Al).
Theoretical = 25 g; actual = 20 g. Find percent yield.
(20 ÷ 25) × 100 = 80%
Explain why the mass of products equals the mass of reactants.
Law of Conservation of Mass—matter is not created or destroyed.