Here are the steps to solve this problem: 1) Balance the equation: Zn + I2 → ZnI2 2) Convert given mass of Zn to moles: 125.0 g Zn → 2.25 mol Zn (molar mass = 65.38 g/mol) 3) Use mole ratio from balanced equation: 2.25 mol Zn → 2.25 mol ZnI2 4) Convert moles of ZnI2 to grams: 2.25 mol ZnI2 x 143.32 g/mol = 322.5 g ZnI2 So the mass of ZnI2 produced from 125.0 g of Zn is 322.5 g.

1. Chapter 12 - Stoichiometry
I ‘m back!
Objective: To learn how to use a complete
chemical equation to calculate quantities of a
substance

2. Chemical Equations
 Remember that a balanced chemical equation
provides the same kind of quantitative
information that a recipe does.
 From the specific amounts of the ingredients, a
specific amount of cookies can be made.
 Due to this, proportional relationships b/w the
ingredients and the products can be written.
 What would happen if you add more or less of 1
ingredient?

3. Proportional Relationships
2 1/4 c. flour 3/4 c. brown sugar
1 tsp. baking soda 1 tsp vanilla extract
1 tsp. salt 2 eggs
1 c. butter 2 c. chocolate chips
3/4 c. sugar Makes 5 dozen cookies.
1) 1 tsp. baking soda = 2 c. chocolate chips
2) 1 c butter= 2 eggs
3) 5 dz cookies = 1tsp. Salt
4) 5 dz cookies = ¾ c. sugar
ETC.

4. Proportional Relationships
2 1/4 c. flour 3/4 c. brown sugar
1 tsp. baking soda 1 tsp vanilla extract
1 tsp. salt 2 eggs
1 c. butter 2 c. chocolate chips
3/4 c. sugar Makes 5 dozen cookies.
I have 5 eggs. How many cookies can I make?
Ratio of eggs to cookies
5 eggs 5 doz.
= 12.5 dozen cookies
2 eggs

5. Stoichiometry
x Stoichiometry - The study of quantities of
materials consumed & produced in chemical
reactions.
• Uses a balanced chemical equation
• Similar to bookkeeping.
• Based on MOLE RATIOS

6. Interpreting Balanced Equations
2H2 + O2 → 2H2O
 2 molecules of hydrogen and 1 molecule of
oxygen form 2 molecules of water.
 2 dozen molecules hydrogen and 1 dozen
molecules of oxygen form 2 dozen molecules
of water.
 2 moles of hydrogen and 1 mole of oxygen
form 2 moles of water.

7. Mole Ratio tells the ratio between 2 substances
in a balanced chemical equation.
• indicated by coefficients in a balanced equation
• Ex. 2 Mg + O2 → 2 MgO
2 moles Mg 1 mole O2
or
2 moles Mg
1 mole O2
2 moles MgO 2 mole Mg
2 mole Mg or 2 moles MgO
2 moles MgO
1 mole O2
or
1 mole O2 2 moles MgO

8. LAW of CONSERVATION of MASS
The MOLE relationships can also apply to mass
relationships. We can check this converting from grams
to moles.
2H2 + O2 → 2H2O
Reactants:
2.02 g H2
2 moles H2 = 4.04 g H2
1 mole H2
1 mole O2 32.00 g O2 = 32.00 g O2
36.04 g H2 + O2
1 mole O2
Product:
18.02 g H2O = 36.04 g H2O
2 moles H2O 1 mole H O
2

9. Steps to Calculate
Stoichiometric Problems
1. Correctly balance the equation.
2. Convert the given amount into
moles.
3. Set up mole ratios.
4. Use mole ratios to calculate moles
of desired chemical.
5. Convert moles back into final unit.

10. Types of Calculations
Remember the mole ratio is the ratio between
any two substances in a reaction and will be
used in all calculations
1. mole to mole
Ex. 1 How many moles of O2 are produced when
3.34 moles of Al2O3 decompose?
2 Al2O3 → 4Al + 3O2
3.34 mol Al2O3 3 mol O2 = 5.01 mol O2
2 mol Al2O3

11. *Practice problem 1:
C2H2 + O2 → CO2 + H2O (unbalanced)
If 3.84 moles of C2H2 are burned, how many
moles of O2 are needed?

12. types of problems (continued)
2. moles to grams
given moles  mole ratio  molar mass
Ex. 2 If 1.50 moles of Fe are used , how
many grams of copper II sulfate would form?
2Fe + 3CuSO4 → Fe2(SO4)3 + 3Cu
1.50 mol of Fe 3 mol CuSO4 159.62 g CuSO4
2 mol Fe 1 mol CuSO4
= 359 g CuSO4

13. *Practice problem 2:
C2H2 + O2 → CO2 + H2O
If 0.750 moles of O2 are used, how many grams of
C2H2 are burned?
3. grams to moles
given mass  molar mass  mole ratio
Ex. 3 If 146 g of NaCl are produced in the following
reaction, how many moles of Cl2 were consumed?
2Na + Cl2  2NaCl
146 g NaCl 1 mol NaCl 1 mol Cl2 = 1.25 mol
58.44 g NaCl 2 mol NaCl

14. *Practice problem 3: Calculate the no. of moles
of CH4 used to produce 1.8 g of H2O.
CH4 + 2O2 → CO2 + 2H2O
types of problems (continued)
4. grams to grams
given mass  molar mass  mole ratio molar mass
Ex. 4 If 10.8 g of Fe are added to a solution of
CuSO4, how many grams of solid copper would
form? 2Fe + 3CuSO4 → Fe2(SO4)3 + 3Cu
10.8 g Fe 1 mol Fe 3 mol Cu 63.55 g Cu = 18.4g
55.85 g Fe 2 mol Fe 1 mol Cu

15. *Practice problem 4: Zinc reacts with
iodine to form zinc iodide (ZnI2). Write the
balanced equation for this reaction.
Calculate the grams of ZnI2 that would be
produced from a 125.0 g sample of Zn.