Wednesday January 23, 2013
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Transcript of Wednesday January 23, 2013
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WednesdayJanuary 23, 2013
(What is Stoichiometry?; Mole
Ratios)
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Bell RingerWednesday, 1-23-13
Sodium metal reacts with chlorine gas to produce sodium chloride.
Write the balanced chemical equation.
Na + Cl2 æ NaCl22What do the blue balance numbers really
mean?The blue balance numbers represent either
the number of particles of each substance or the number of moles of each substance.
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AnnouncementsHappy National Pie
Day!
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AnnouncementsI will not be available
after school today.
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Assignment Currently Open
Summative or
Formative?Date
Issued Date Due Date Into GradeSpeed Final Day
QUIZ 15 S5 1/11 1/15 1/29
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Stoichiometry
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What is Stoichiometry?
Stoichiometry involves the quantity relationships between reactants and
products in a chemical reaction.
Stoichiometry is used when you have a problem where you are given the
quantity of one substance and you need to determine the quantity of another
substance.
Stoichiometry can be used to determine how much of a substance to start with as a reactant, or how much of a substance
will be produced in a reaction.
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What is Stoichiometry?All reaction stoichiometry calculations start with a
balanced chemical equation.
The coefficients (balance numbers) of the equation
represent the relative numbers of moles of
reactants and of products.
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It is extremely important to recognize what the coefficients of a balanced chemical equation represent.
These coefficients can be interpreted to represent two different things:
– the number of particles of each substance in the reaction.
or– the number of moles of each substance in the reaction.
For example, consider the balanced equation below:
H2 + O2 → H2OThis can be interpreted as 2 molecules of hydrogen
gas react with 1 molecule of oxygen gas to produce 2 molecules of water.
or2 moles of hydrogen gas react with 1 mole of oxygen
gas to produce 2 moles of water.
The Dual Meanings of Coefficients
22
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A mole ratio is a conversion factor that relates the amounts in moles of any two substances involved in a
chemical reaction.Mole ratios use the coefficients from a balanced chemical
equation.Example: aluminum oxide decompose to produce aluminum and oxygen gas. Write and balance the
equation.
Al2O3 → Al + O2
This means that 2 moles of aluminum oxide decompose to produce 4 moles of aluminum and 3 moles of oxygen gas.
The mole ratio of Al2O3 to Al is 2:4, or 1:2
The mole ratio of Al2O3 to O2 is 2:3
The mole ratio of Al to O2 is 4:3
Mole Ratios
2 4
3
2
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Sample ProblemWhat are the mole ratios when cadmium (II) metal
reacts with hydrobromic acid to produce cadmium (II) bromide and hydrogen gas.
First, Write and balance the equation.
Cd + HBr æ CdBr2 + H2This means that 1 mole of cadmium reacts with 2 moles of hydrobromic acid to produce 1 mole of cadmium (II)
bromide and 1 mole of hydrogen gas.
What is the mole ratio of Cd to H2? 1:1
What is the mole ratio of HBr to CdBr2? 2:1
What is the mole ratio of CdBr2 to H2? 1:1
Mole Ratios
2
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WorksheetIntroduction to Stoichiometry
and Mole Ratios