1. Calculating Quantities in Reactions
Stoichiometry
Table of Contents
Calculating Quantities in Reactions
Mole-to-mass and Mass-to-mass problems
Limiting Reactants and Percentage Yield

2. Mole to mass and mass to mass problems
Bellringer
In a spacecraft, the carbon dioxide exhaled by astronauts can be removed by its reaction with lithium hydroxide, LiOH, according to the following chemical equation.
CO2(g) + 2LiOH(s) → Li2CO3(s) + H2O(l)
How many moles of lithium hydroxide are required to react with 20 mol CO2, the average amount exhaled by a person each day?

3. Bellringer CO2(g) + 2LiOH(s) → Li2CO3(s) + H2O(l)
Mole to mass and mass to mass problems
Bellringer
CO2(g) + 2LiOH(s) → Li2CO3(s) + H2O(l)
Mol LiOH= 20 mol CO2 x 2 mol LiOH = 40 mol LiOH
1 mol CO2

4. Solving Stoichiometry Problems
Mole to mass and mass to mass problems
Solving Stoichiometry Problems
Gather information.
Determine the balanced equation for the reaction.
Write an equality using substances and their coefficients.
Plan your work.
Think through the three basic steps :
change to moles
use the mole ratio
change out of moles
Find the conversion factors for each step.

5. Solving Stoichiometry Problems
Mole to mass and mass to mass problems
Solving Stoichiometry Problems
Write the mole ratio:
Calculate.
Write a “?” with the units of the answer followed by “=“ and the quantity of the given substance.
Write the conversion in order so that you change the units of the given substance to the units needed.
Cancel units and check that the remaining units are the required of the unknown substance.

6. Solving Mass-Mass Problems
Mole to mass and mass to mass problems
Solving Mass-Mass Problems

7. Problems Involving Mass
Mole to mass and mass to mass problems
Problems Involving Mass
Sample Problem B
What mass of NH3 can be made from 1221 g H2 and excess N2?
N2 + 3H NH3

8. Problems Involving Mass, continued
Mole to mass and mass to mass problems
Problems Involving Mass, continued
mass of H2 = 1221 g H2
molar mass of H2 = 2.02 g/mol
mass of NH3 = ? g NH3
molar mass of NH3 = g/mol
3 mol H2 = 2 mol NH3 (From the equation)
To change grams to moles, use the molar mass of H2.

9. Problems Involving Mass, continued
Mole to mass and mass to mass problems
Problems Involving Mass, continued
The mole ratio must cancel out the units of mol H2 given in the problem and leave the units of mol NH3. Therefore, the mole ratio is
To change moles of NH3 to grams, use molar mass of NH3.

10. Interpreting Graphics
Chapter 9
Standardized Test Preparation
Interpreting Graphics
13. If the reaction that fills the air bag is the decomposition of sodium azide, represented by the equation, 2NaN3(s) 2Na(s) + 3N2(g), how many moles of products are produced by the decomposition of 3.0 moles of sodium azide?

11. Interpreting Graphics
Chapter 9
Standardized Test Preparation
Interpreting Graphics
13. If the reaction that fills the air bag is the decomposition of sodium azide, represented by the equation, 2NaN3(s) 2Na(s) + 3N2(g), how many moles of products are produced by the decomposition of 3.0 moles of sodium azide?
Answer: 7.5 mol