STOICHIOMETRY
Definition:
stoi·chi·om·e·try (stoi'kē-ŏm'ĭ-trē)
 Calculation of the quantities of reactants and products in a chemical reaction.
 The quantitative relationship between reactants and products in a chemical reaction.
To perform a stoichiometric calculation, information about a chemical reaction must be given or you must acquire the information
by completing a laboratory investigation. The following information is necessary to perform a stoichiometric calculation:
1.
2.
3.
4.
5.
6.
Know the reactants and products of the reaction
Write correct chemical formulas for all reactants and products
Write a skeletal equation that describes the chemical reaction
Balance the skeletal equation
Identify amount of reactant or product given in problem or measured during lab
Identify the target reactant or product
Once the above information is known, carry out the following steps:
7.
8.
9.
10.
Be sure you have a correctly balance chemical equation.
Take the given or measured quantity and convert it to moles (see previous handouts).
Set up a mole to mole ratio of the target material to the given material.
Change target material moles to desired units (see previous handout). This is a theoretical quantity.
Below is a sample problem that illustrates the process.
In a lab experiment Lulu and Larry wanted to determine the quantity of lead(II) iodide that would theoretically be produced
when potassium iodide was mixed with lead(II) nitrate. They measured out a 1.56-g sample of lead(II) nitrate, dissolved it in
water, and then added an excess of potassium iodide solution. A yellow precipitate of lead(II) iodide was formed along with a
solution of potassium nitrate. How many grams of lead(II) iodide did Lulu and Larry expect to get?
Step 1:
The reactants were lead(II) nitrate and potassium iodide.
The products were lead(II) iodide and potassium nitrate.
Step 2:
The formulas for the reactants and products are”
 lead(II) nitrate
Pb(NO3) 2
 potassium iodide
KI
 lead(II) iodide
PbI2
 potassium nitrate
KNO3
Step 3:
Pb(NO3) 2 +
KI
PbI2 + KNO3
Pb(NO3) 2 +
2 KI
PbI2 + 2 KNO3
Step 4:
Step 5:
1.56 grams of lead(II) nitrate was measured by Lulu and Larry
Step 6:
Lead(II) iodide is the target material
Now it is time to set up the calculation format using step 7 through 10.
Step 7:
We already have a balanced equation. See Step 4.
Step 8: Change given quantity to moles. Skip this step if the given quantity is already given in moles.
Step 9: Use mole ratio to change moles of the given material to target material. Use the coefficients of the balanced equation.
Step 10: Convert the target quantity of moles to desired units.
Complete the mathematical calculation.