AP Chemistry / Unit 4: Chemical Reactions
4.5 Stoichiometry
Notes
grams → moles → mole ratio → moles → grams.
- The limiting reactant runs out first and sets the theoretical yield.
- Percent yield = actual ÷ theoretical × 100.
Practice
$2H_2+O_2\to2H_2O$. 4 mol $\mathrm{H_2}$ make how many mol $\mathrm{H_2O}$?
1:1 ratio.
2 mol $\mathrm{H_2}$ and 2 mol $\mathrm{O_2}$ react. The limiting reactant:
$\mathrm{H_2}$ needs only 1 mol $\mathrm{O_2}$.
Theoretical yield 20 g, actual 15 g. Percent yield:
$\displaystyle \frac{15}{20}$.
Ready for more? Take the Unit 4 test.