- Let's start with how to say this word. Five syllables -STOY-KEE-AHM-EH-TREE.
- It's a big word that describes a simple idea. Stoichiometry is the part of chemistry that studies amounts of substances that are involved in reactions. You might be looking at the amounts of substances before the reaction. You might be looking at the amount of material that is produced by the reaction. Stoichiometry is all about amounts.
- Balanced chemical equations are required. Because they tell us the ratio of the molecules or moles of the substances in a chemical reaction.
Example
Propane (C₃H₈)
is the fuel used in most gas grills. It burn according
to the balanced equation
C₃H₈ + 5O₂ ---> 4H₂O
+ 3CO₂
If you burn 215 g of propane, how many
grams of H₂O will be produced?
215gC₃H₈ x (1mol C₃H₈/44.0gC₃H₈) x (4mol H₂O/1mol C₃H₈) x (18.0gH₂O/1mol H₂O)=325gH₂O
Molarity and Stoichiometrty
Example
For the
reaction: Zn + 2HCl ₂ ---> ZnCl₂ + H₂
How many mL of 0.500 M HCl are needed
to react with 2.00 grams of Zn?
2.00gZn x (1mol Zn/654gZn) x (2mol HCl/1mol Zn)x(1L HCl/0.500mol HCl) x (1000mL HCl/1L HCl) = 122mL HCl
Gas Stoichiometry
Hydrogen gas (and NaOH) is produced when sodium metal is added to water. What mass of Na is needed to produce 20.0 L of H2 at STP?
First we need a balanced equation:
2Na(s) + 2H2O(l) ----> H2(g) + 2NaOH(aq)
Then we can calculate the mass of Na:
20.0L H2 * 1mole/22.4L*2mole Na/1mole H2*23.0g/1mole Na=41.1gNa
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