1. Chapter 12
Stoichiometry

2. Stoichiometry The branch of chemistry that deals
with the mass relationships of elements in compounds
and
the mass relationships between reactants and products in a chemical reaction.

3. Composition Stoichiometry
Stoichiometry that deals with the mass relationships of elements in compounds

4. Reaction Stoichiometry
Stoichiometry involving the mass relationships between reactants and products in a chemical reaction

5. Equations are the recipes that tell chemists
what amounts of reactants to mix and
what amounts of products to expect.
The quantities of reactants and products -----come from the balanced equation.

6. When you know the quantity (grams or moles) of one substance in a reaction,
you can calculate the quantity of any other substance consumed or created in the reaction.

7. Calculations using balanced equations are called stoichiometric calculations.
For chemists, stoichiometry is a form of bookkeeping.

8. INTERPRETING CHEMICAL EQUATIONS
N2(g) + 3H2(g) 2NH3(g)
1 mol of nitrogen reacts with 3 mol of hydrogen to form 2 mol of ammonia.

9. Reaction – Stoichiometry Problems
Begin with a balanced chemical equation!!!

10. Mole-Mole Calculations
The coefficients from the balanced equation are used to write conversion factors called mole ratios.

11. Three of the mole ratios for this equation are
1 mol N mol NH3 3 mol H2
3 mol H mol N2 2 mol NH3

12. Reaction – Stoichiometry Problems
Identify the information given
Identify the unknown, the information you are expected to find.
Given  Unknown

13. Unknown amount in moles
Given amount in moles
 Mole to Mole Ratio
Unknown amount in moles

14. Thus a general solution for a mole-mole problem is given by
From balanced equation
x mol G x = mol W
b mol W xb
a mol G a
Given Mole ratio Calculated

15. How many moles of ammonia are produced when 0
How many moles of ammonia are produced when 0.60 mol of nitrogen reacts with hydrogen?
2 mol NH3
1 mol N2
0.60 mol N2 x
= mol NH3
Given
Mole Ratio

16. Problem
In a spacecraft, the carbon dioxide exhaled by astronauts can be removed by its reaction with lithium hydroxide.
CO2(g) + 2 LiOH(s)  Li2CO3(s) + H2O (l)
How many moles of lithium hydroxide are required to react with 20 moles of CO2, the average amount exhaled by a person each day?

17. Answer
20 mole CO2
x 2 mole LiOH
1 mole CO2
= 40 mole LiOH