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

2. What is the percentage composition of NH4I?
Calculating Quantities in Reactions
Bellringer
What is the percentage composition of NH4I?
Molar mass= x(1) + 127= 145 g/mol
N  14/145*100 = 9.6 %
H  4/145*100 = 2.8 %
I  127/145*100 = 87.6

3. Balanced Equations Show Proportions
Calculating Quantities in Reactions
Balanced Equations Show Proportions
The proportions of the ingredients in a muffin recipe let you adjust the amounts to make enough muffins even if you do not have balanced amounts initially.
In a balanced chemical equation coefficients show the proportions of the reactants and products.

4. Balanced Equations Show Proportions
Calculating Quantities in Reactions
Balanced Equations Show Proportions
2H2 + O2  2H2O
The coefficients show that two molecules of hydrogen react with one molecule of oxygen and form two molecules of water.
Calculations involving chemical reactions use the proportions from balanced chemical equations to find the quantity of reactants and products involved.

5. Balanced Equations Show Proportions
Calculating Quantities in Reactions
Balanced Equations Show Proportions
For each problem in this section, assume that there is more than enough of all other reactants to completely react with the reactant given.
Also assume that every reaction happens perfectly, so that no product is lost during collection.

6. Calculating Quantities in Reactions
Relative Amounts in Equations Can Be Expressed in Moles
The branch of chemistry that deals with quantities of substances in chemical reactions is known as stoichiometry.

7. Calculating Quantities in Reactions
Relative Amounts in Equations Can Be Expressed in Moles
The coefficients in a balanced equation also represent the moles of each substance.
For example, the equation below shows that 2 mol H2 react with 1 mol O2 to form 2 mol H2O.
2H2 + O2  2H2O

8. Using Mole Ratios Sample Problem A N2 + 3H2  2NH3
Calculating Quantities in Reactions
Using Mole Ratios
Sample Problem A
A mole ratio is a conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction.
Consider the reaction for the commercial preparation of ammonia.
N2 + 3H2  2NH3
How many moles of hydrogen are needed to prepare 312 moles of ammonia?

9. N2 + 3H2  2NH3 Using Mole Ratios Sample Problem A Solution
Calculating Quantities in Reactions
Using Mole Ratios
Sample Problem A Solution
amount of NH3 = 312 mol
amount of H2 = ? mol
3 mol H2 = 2 mol NH3
The mole ratio must cancel out the units of mol NH3 given in the problem and leave the units of mol H2.
Therefore, the mole ratio is
N2 + 3H2  2NH3

10. Using Mole Ratios, continued
Calculating Quantities in Reactions
Using Mole Ratios, continued
Sample Problem A Solution, continued

11. Understanding Concepts
Exit Slip
Understanding Concepts
What is the mole ratio of CO2 to C6H12O6 in the combustion reaction:
C6H12O6 + 6O CO2 + 6H2O?
A. 1:1
B. 1:2
C. 1:6
D. 6:1