1. Stoichiometry The Arithmetic of Equations
Prentice-Hall Chapter 12.1
Dr. Yager

2. Objectives
Explain how balanced equations apply to both chemistry and everyday situations.
Interpret balanced chemical equations in terms of moles, representative particles, mass, and gas volume at STP.
Identify the quantities that are always conserved in chemical reactions.

3. A balanced chemical equation provides the same kind of quantitative information that a recipe does.

4. Here is the Problem! Cupcake Recipe for 10 cupcakes: 2 eggs
3 cups of flour
1 cup sugar
You have:
3 eggs
4 cups of flour
2 cups of sugar
What limits the number of cupcakes you can make?

5. The original recipe is: 2:3:1
2 eggs, 3 C flour, 1 C sugar
Given: eggs, 4 C flour, 2 C sugar
3 eggs requires:
4.5 cups of flour and 1.5 cups of sugar
4 cups of flour requires:
2 2/3 eggs and 1 1/3 cups of sugar
2 cups of sugar requires:
4 eggs and 6 cups of flour
The only one possible is #2!

6. The Chemist:
Uses the ratio or balanced equation to calculate how much reactant is needed or product formed.
The calculation of quantities in chemical reactions is a subject of chemistry called stoichiometry.

7. Stoichiometry
Defined as the calculation of quantities in chemical reactions
Form of bookkeeping for chemists
Generally, one of the reactants limits the calculations

8. An equation can represent the manufacturing of a single tricycle.

10. A balanced chemical equation can be interpreted in terms of different quantities, including numbers of atoms, molecules, or moles; mass; and volume.

11. Interpreting Chemical Equations
N2(g) + 3H2(g) NH3(g)

12. Atoms, Molecules, etc..

13. Moles

14. Mass

15. Volume

16. What is Conserved? Mass and atoms are conserved.
Molecules, formula units, moles and volumes are not necessarily conserved.
Example where they are conserved:
H2(g) + I2(g) HI(g)

17. Balance and Tell What is Conserved
C2H2 (g) + O2 (g) CO2 (g) + H2O(g)
2C2H2 (g) + 5O2 (g) CO2(g) + 2H2O(g)
Atoms – Yes Mass - Yes
Molecules – No Formula Units – No
Moles – No Volume – No

20. 1. A manufacturer of bicycles has 5350 wheels, 3023 frames, and 2655 handlebars. How many bicycles can be manufactured using these parts?
2675 bicycles
2655 bicycles
3023 bicycles
5350 bicycles

21. 1. A manufacturer of bicycles has 5350 wheels, 3023 frames, and 2655 handlebars. How many bicycles can be manufactured using these parts?
2675 bicycles
2655 bicycles
3023 bicycles
5350 bicycles

22. 2. A reaction that produces iron metal from iron ore:
Fe2O3•H2O(s) + 3CO(g)  2Fe(s) + 3CO2(g) + H2O(g)
What is the volume of gas at STP that reacts and the volume of gas at STP produced?
3 L and 4 L.
67.2 L and 89.6 L.
67.2 L and 67.2 L
3 L and 3 L

23. 2. A reaction that produces iron metal from iron ore:
Fe2O3•H2O(s) + 3CO(g)  2Fe(s) + 3CO2(g) + H2O(g)
What is the volume of gas at STP that reacts and the volume of gas at STP produced?
3 L and 4 L.
67.2 L and 89.6 L.
67.2 L and 67.2 L
3 L and 3 L

24. 3. What is conserved in this reaction? H2(g) + Cl2(g)  2HCl(g)
only mass
only mass and number of moles
only mass, number of moles, and number of molecules
mass, number of moles, number of molecules, and volume

25. 3. What is conserved in this reaction? H2(g) + Cl2(g)  2HCl(g)
only mass
only mass and number of moles
only mass, number of moles, and number of molecules
mass, number of moles, number of molecules, and volume