C. Johannesson

Stoichiometric Calculations

Stoichiometry – Ch. 9

C. Johannesson

A. Proportional Relationships

• I have 5 eggs. How many cookies can I make?

3/4 c. brown sugar1 tsp vanilla extract2 eggs2 c. chocolate chipsMakes 5 dozen cookies.

2 1/4 c. flour1 tsp. baking soda1 tsp. salt1 c. butter3/4 c. sugar

5 eggs 5 doz.

2 eggs= 12.5 dozen cookies

Ratio of eggs to cookies

C. Johannesson

A. Proportional Relationships

• Stoichiometry–mass relationships between substances

in a chemical reaction–based on the mole ratio

• Mole Ratio– indicated by coefficients in a balanced

equation

2 Mg + O2 2 MgO

C. Johannesson

B. Stoichiometry Steps1. Write a balanced equation.2. Identify known & unknown.3. Line up conversion factors.

–Mole ratio - moles moles–Molar mass - moles grams

Core step in all stoichiometry problems!!

4. Check answer.

C. Johannesson

Stoichiometry Problems• How many moles of KClO3 must

decompose in order to produce 9 moles of oxygen gas?

9 mol O2 2 mol KClO3

3 mol O2

= 6 mol KClO3

2KClO3 2KCl + 3O2 ? mol 9 mol

C. Johannesson

D. Stoichiometry Problems• How many grams of silver will be

formed from 12.0 g copper?

12.0g Cu

1 molCu

63.55g Cu

= 40.7 g Ag

Cu + 2AgNO3 2Ag + Cu(NO3)2

2 molAg

1 molCu

107.87g Ag

1 molAg

12.0 g ? g