Stoichiometry
Chapter 12
Stoichiometry
• STOY-KEE-AHM-EH-TREE
– Founded by Jeremias Richter, a German chemist
– Greek orgin
• stoikheion – element & metron – measure
• The branch of chemistry that deals with the
quantities of substances that enter into, and are
produced by, chemical reactions.
• Shows the quantitative relationship between
reactants and products in a chemical reaction.
– How much product is formed from a given amount of
reactants.
Balanced Chemical Equation (BCE)
• Coefficients are used to balance chemical
equations.
• The BCE illustrates that chemical reactions
follow Law of Conservation of Mass
– The number and types of atoms on the reactants
side is equal to the number and types of atoms on
the products.
– Reactants (left)Products (right)
The coefficients are molar ratios of reactants
and products.
We can use the molar ratios to convert from
one substance to another using Stoichiometry
Stoichiometry Problems
• Each problem will be 3 steps
1. Convert 2. Mole to mole
ratio
using
to moles
3. Convert to
required
unit.
balanced chemical
equation (BCE)
BCE
Example
• What is the mass of Al2O3 that can be made
from 25 grams of aluminum?
• Balanced Equation: 4 Al + 3 O2  2 Al2O3
BCE
You Should Know About Stoichiometry
1. You have to use units to understand the process
2. Units include g, mol, L, particles AND chemical formulas
3. Convert your given to moles
4. You have to use units to understand the process
5. Use BCE coefficients to convert from one substance to another
6. You have to use units to understand the process
7. Convert answer to required unit
8. You have to use units to understand the process
9. Units include g, mol, L, particles AND chemical formulas
10. It is not that hard 
Percent Yield
• Indicates the percent of theoretical yield that was
obtained from the final product in an experiment.
• The closer to 100% the better
• Percent Yield = actual mass x 100
theoretical mass
Percent Error
• Percent Error = (actual mass – theoretical mass) x 100
theoretical mass
• The lower the percent error the better
Limiting Reactants
• The limiting reactant is the reactant present in the
smallest stoichiometric amount
– In other words, it’s the reactant you’ll run out of first
Hydrogen is limiting
Hydrogen is limiting
5N2 and 9H2
6NH3 and 2N2
How 2 Calculate the
Limiting Reactant
• Convert each of the given reactants to a product
• The reactant that produces the least product is the
limiting reactant.
Example:
• Nickel replaces silver from silver nitrate in solution according to the following
equation: 2AgNO3 + Ni → 2Ag + Ni(NO3)2 If you have 22.9 g of Ni and 112 g of
AgNO3 ,what mass of nickel(II) nitrate would be produced?
• 22.9g Ni x 1 mol Ni x 1 mol Ni(NO3)2 x 182.7g Ni(NO3)2 = 71.3 g Ni(NO3)2
58.7g Ni
1 mol Ni
1 mol Ni(NO3)2
• 112 g AgNO3 x 1 mol AgNO3 x 1 mol Ni(NO3)2 x 182.7g Ni(NO3)2 = 60.2 g Ni(NO3)2
169.9g AgNO3 2 mol AgNO3
1 mol Ni(NO3)2
• AgNO3 is limiting & 60.2 g Ni(NO3)2 can be produced
Limiting Reactant Challenge
• Given 20 mL HCl (1.46g HCl) calculate the amount of
Mg to add to generate the maximum production of
Hydrogen gas with Mg still limiting the reaction.
• Calculate the percent yield of Hydrogen gas