Chapter 3 - Stoichiometry
It is important to be able to quantify
the amount of reagent(s) that will be
needed to produce a given amount of
product(s). The science of quantifying
substances involved in chemical
reactions is called Stoichiometry.
Writing Chemical Equations
• The Basics of Writing Reactions
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An arrow is used to indicate reaction progress.
Reactants on the left, products on the right.
Use a ‘+’ sign between reagents and products.
Use a subscript to indicate the state of
substances.
Writing Chemical Equations
• The Basics of Writing Reactions
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How can you predict the state of a substance in a
chemical reaction?
Use your knowledge of chemistry
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Covalent compounds are usually gases.
If an ionic compounds reacts with another ionic
compound, then they must be aqueous.
Water is a liquid unless the reaction produces a lot of
heat.
Writing Chemical Equations
• The Basics of Writing Reactions
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Coefficients are whole numbers in front of
substances to indicate the number of particles
present in the reaction.
Writing Chemical Equations
• Balancing Chemical Reactions
o Use coefficients to follow the Law of
Conservation of Mass
__Na2S(aq) + __BaNO3(aq)  __NaNO3(aq) + __BaS(s)
__C8H18(g) + __O2(g) __H2O(g) + __CO2(g)
Writing Chemical Equations
• Balancing Chemical Reactions
o Write the following chemical reactions then
balance them;
o Iron reacts with oxygen gas to produce iron(III) oxide.
o Electricity can break down water into oxygen gas and
hydrogen gas by a process called electrolysis.
Writing Chemical Equations
• Balancing Chemical Reactions
o Write the following chemical reactions then
balance them;
o Ethane reacts with oxygen gas to produce water vapor
and carbon dioxide.
o Calcium nitrate and lithium chloride react to produce
soluble lithium nitrate and a white precipitate called
calcium chloride.
Writing Chemical Equations
• Simple Chemical Reactions
o Synthesis (Combination) Reactions;
o When two atoms or molecules combine to form a
larger compound.
N2(g) + 3H2(g)  2NH3(g)
Writing Chemical Equations
• Simple Chemical Reactions
o Synthesis (Combination) Reactions;
o Write the chemical reaction in which sodium metal
reacts with oxygen gas.
Writing Chemical Equations
• Simple Chemical Reactions
o Decomposition Reactions;
o A compound breaks apart into two smaller molecules
or atoms;
2H2O2(l)  2H2O(g) + O2(g)
Writing Chemical Equations
• Simple Chemical Reactions
o Decomposition Reactions;
o Write the decomposition of carbonic acid into water
and carbon dixoide;
Writing Chemical Equations
• Simple Chemical Reactions
o Combustion Reactions;
o Combustion occurs when oxygen gas is consumed in a
chemical reaction and is combined to all products.
Writing Chemical Equations
• Simple Chemical Reactions
o Combustion Reactions;
o Combustion occurs when oxygen gas is consumed in a
chemical reaction and is combined to all products.
Writing Chemical Equations
• Simple Chemical Reactions
o Combustion Reactions;
o Write the chemical equation for the combustion of
hexane.
Writing Chemical Equations
• Empirical Formulas
o A reduced version of the ratio of atoms in a
compound.
C10H22 (molecular formula) 
C5H11 (empirical formula)
Writing Chemical Equations
• Empirical Formulas
o We can calculate an empirical formula if we know the
percent by mass of the elements in a compound.
Percent by Mass = mass of element in compound x 100
total mass of compound
Writing Chemical Equations
• Empirical Formulas
o Calculate the percent mass of each element in the
compound C6H12.
o Calculate the emprical formula of this compound.
Writing Chemical Equations
• Empirical Formulas
o Calculate the molar mass of the compound if its
molecular weight is 84.18 g/mol.
Writing Chemical Equations
• Avogadro’s Number – The Mole
o Amedeo Avogadro (1600’s)
o Developed a way to quantify gas particles.
o Calculated that a container that had a volume
of 22.4L would contain 6.02 x 1023 gas
particles.
Writing Chemical Equations
• The Mole
o Relates the mass of a substance with the
number of representative particles and molar
volume.
Writing Chemical Equations
• Mole Conversions
o Convert 20.0 grams of NaCl
into moles.
o Convert 0.35 moles of carbon tetrabromide into
grams.
Writing Chemical Equations
• Mole Conversions
o Convert 10.0 L of CO2 into moles
at STP.
o Convert 1.80 moles of ammonia into liters.
Writing Chemical Equations
• Mole Conversions
o Convert 5.63 x 1015 atoms of iron
into moles.
o Convert 0.0025 moles of magnesium atoms into
moles.
Writing Chemical Equations
• Mole Conversions
o Convert 1.2 x 1025 molecules of
oxygen gas into grams.
o Convert 500.0 Liters of nitrogen dioxide into grams.
Writing Chemical Equations
• Stoichiometric Conversions
Writing Chemical Equations
• Stoichiometric Conversions
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Molar Ratios – A conversion factor
constructed from the coefficients of a
balanced chemical reaction.
O2(g) +2H2(g)  2H2O(g)
Writing Chemical Equations
• Stoichiometric Conversions
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What volume of water vapor can be
produced if 10.00 grams of oxygen gas reacts with an
excess of hydrogen gas?
O2(g) +2H2(g)  2H2O(g)
Writing Chemical Equations
• Stoichiometric Conversions
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How many grams of lead(II)iodide
can be produced if 5.00 grams of potassium iodide
reacts with an excess of lead(II)nitrate?
2KI(aq) + Pb(NO3)2(aq)  2KNO3(aq) + PbI2(s)
Writing Chemical Equations
• Limiting Reactants
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1.00 gram of iron is allowed to react with 1.00 gram of
nitrogen gas to form iron(II)nitride.
3Fe(s) + N2(g)  Fe3N2(s)
Which is the limiting reagent?
What mass of iron(II)nitride will be produced?
Writing Chemical Equations
• Limiting Reactants
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1.00 gram of iron is allowed to react with 1.00 gram of
nitrogen gas to form iron(II)nitride.
3Fe(s) + N2(g)  Fe3N2(s)
Which is the reagent in excess?
What mass of the reagent in excess will remain after the
reaction has stopped?
Writing Chemical Equations
• Limiting Reactants
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Tin and nitric acid will react to form tin(IV)oxide,
nitrogen dioxide, and water. 8.00 grams of nitric acid
is added to a 20.0 gram sample of tin.
What volume of nitrogen dioxide will be collected at STP?
Writing Chemical Equations
• Limiting Reactants
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Tin and nitric acid will react to form tin(IV)oxide,
nitrogen dioxide, and water. 8.00 grams of nitric acid
is added to a 20.0 gram sample of tin.
What mass of the reagent in excess will remain after the
reaction has stopped?
Writing Chemical Equations
• Calculating Percent Yield
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The percent yield of a chemical reaction is a measure
of its efficiency.
% yield = Actual Amount Recovered x 100
Theoretic Amount
Writing Chemical Equations
• Calculating Percent Yield
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100.0 mL of fluorine gas is bubbled through a solution
that contains 4.00 grams of calcium bromide. Calcium
fluoride and 1.5 grams of liquid bromine is produced.
Calculate the percent yield of this chemical reaction.