Stoichiometry
“Calculating Quantities in Reactions”
• The coefficients in a balanced chemical equation
represent the numbers of particles for each substance in
the reaction.
2H2 + O2  2H2O
• For this equation, the coefficients show that _____
molecules of hydrogen react with _____ molecules of
oxygen to yield _____ molecules of water.
Balanced Equations Show
Proportions
• Just as you can interpret these equations in terms of
particles, you can interpret them in terms of moles.
• The coefficients in a balanced equation also represent the
moles of each substance.
2C8H18 + 25O2  16CO2 + 18H2O
How many moles of octane react? ______________
How many moles of oxygen react? ______________
How many moles of CO2 are produced? ______________
How many moles of water are produced? ______________
Amounts in Moles
• Stoichiometry – the proportional relationship between
two or more substances during a chemical reaction.
• You will soon be able to determine how much of a
product is formed from a given quantity of reactant.
• The mole ratio is the key.
• The coefficients are ratios or conversion factors to convert
between reactants and products. These ratios are called
MOLE RATIOS
Mole Ratios in a Rxn
• Consider the following reaction:
• Phosphoric Acid neutralizes Barium Hydroxide  ??
•
•
•
•
What is the molar ratio of acid to base? __________.
Base to salt? __________. Acid to salt? __________.
Base to acid? __________. Water to acid? __________.
Water to base? __________. Base to water? __________.
Practice With Mole Ratios
• The mole ratios are in ____________, obviously.
• You may ONLY convert between reactants and products
through MOLES using the mole ratio as a conversion
factor.
• Make a T-Chart and solve just as we have done in the past
Making Calculations
Grams of “A”
1 mole of “A”
# of moles of “B”
Molar mass of “B”
(in grams)
Molar mass of
“A”
(in grams)
# of moles of “A”
1 mole of “B”
This process enables us to convert
from one reactant to another, one
reactant to a product, or one product
to another using the molar ratios
from the balanced chemical
equation.
Molar Ratio of “A” to “B”
Order of Operations
• How many moles of water can be produced by the combustion
of 2.45 moles of propane?
Step 1: Write out the balanced reaction.
Step 2: Determine the molar ratio or the starting component and the
ultimate component.
Step 3: Make a chart of relationships and solve.
Practice With Stoich
• Convert 0.85 moles of oxygen gas to grams of oxygen
gas.
• Convert 12.54 grams of pentane (C5H12) to moles of
pentane
Practice with
Conversions
• How many grams of oxygen are required to burn 12.54
grams of pentane (C5H12) to completion?
Practice with
Conversions
___POCl3(l) + ___H2O(l)  ___H3PO4(l) + ___HCl(g)
• How many grams of hydrochloric acid will be produced
from the consumption of 18.45 grams of POCl3?
Stoichiometry Problems
1 POCl3(l) + 3 H2O(l)  1 H3PO4(l) + 3 HCl(g)
• How many grams of hydrochloric acid will be produced
from the consumption of 18.45 grams of POCl3?
• How many grams of phosphoric acid will be produced
with this quantity of POCl3?
Stoichiometry Problems
What volume of H3PO4 forms when 56 mL POCl3
completely react? (density of POCl3 = 1.67 g/mL; density of
H3PO4 = 1.83 g/mL)
1 POCl3(l) + 3 H2O(l)  1 H3PO4(l) + 3 HCl(g)
More Practice
How many grams of C5H8 form from 1.89x1024 molecules
C5H12?
C5H12(l)  C5H8(l) + 2H2(g)
Using Molecules
• Get started on your homework
packet “Calculating Quantities
in Reactions”
• This will be homework and
is due tomorrow 