ADVANCED CHEMISTRY

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ADVANCED CHEMISTRY

• Chapter 3 Stoichiometry

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WHAT IS STOICHIOMETRY?

• Antoine Lavoisier observed that the total mass
  before a reaction is equal to the total mass
  after a reaction.
• This observation was termed the Law of
  Conservation of Mass

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WHAT IS STOICHIOMETRY?

• Stoichiometry is the study of the quantitative
  nature of chemical reactions.
• It is used to balance chemical equations and
  determine molar mass and percent yield of
  products in chemical reactions.

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TOPICS IN STOICHIOMETRY

• Balancing Chemical Equations
• Chemical Reactivity types of reactions
• Weight, Mass and Mole Calculations
• Formula and Balanced Equation Analysis
• Limiting Reactants Conclude w/Lab

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BALANCING CHEMICAL EQUATIONS

• RECAP
• All forward equations are written with reactants
  of the left an products on the right
• Example 2H2 O2 ? 2H2O

4 atoms of H in product
Coefficient means 2 molecules of H2, 4
atoms total
Subscript means 2 atoms of H
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BALANCING CHEMICAL EQUATIONS

• Atoms are neither created or destroyedso all
  equations must be balanced!
• RULES FOR BALANCING EQUATIONS
• Cannot change subscripts
• Can change coefficients

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BALANCING CHEMICAL EQUATIONS

• Examples Balance this equation
• Na(s) H2O(l) ? NaOH(aq) H2(g)

• 2Na(s) 2H2O(l) ? 2NaOH(aq) H2(g)

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Patterns of Chemical Reactivitytypes of reactions

• We can use the periodic table to make predictions
  of chemical reactivity
• Elements in the same group react with other
  compounds in a similar way

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Patterns of Chemical Reactivitytypes of reactions

• Example
• Alkali metals (group 1A elements) react with
  (OH)-, hydroxide, in similar way
• 2K(s) 2H2O(l) ? 2KOH(aq) H2(g)

2Na(s) 2H2O(l) ? 2NaOH(aq) H2(g)
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Patterns of Chemical Reactivitytypes of reactions

• Combustion reactions are rapid reactions that
  produce a flame
• Most of these reactions involve hydrocarbon
  compounds and oxygen as reactants and carbon
  dioxide and water are products
• Example
• C3H8(g) 5O2(g) ? 3CO2(g) 4H2O(l)

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Patterns of Chemical Reactivitytypes of reactions

• Combination and Decomposition
• Reactions
• Combination reactions occur when two or more
  substances react to form one product
• Decomposition reactions occur when one
  substance undergoes a reaction to produce two or
  more substances

For example..
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Patterns of Chemical Reactivitytypes of reactions

• Combination reactions
• A B ? C

Examples C(s) O2(g) ? CO2(g) N2(g) 3H2(g)
? 2NH3(g)
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Patterns of Chemical Reactivitytypes of reactions

• Decomposition reactions
• C ? A B

Examples CaCO3(s) ? CaO(s) CO2(g) 2NaN3(s) ?
2Na(s) 3N2(g)
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Sections 3.3 3.5

• Section 3.3
• Formula and Molecular Weights
• Average Atomic mass
• Percent Composition
• Section 3.4 The Mole
• Molar Mass
• The Mole,
• Interconverting Masses, Moles and of Particles
• Section 3.5 Empirical Formula from Analysis
• Determining formulas through experimentation

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The Atomic Mass Scale
Section 3.3

• The atomic mass scale gives the mass of each
  element relative to the mass of 12C.
• The amu is defined by assigning a mass of 12 amu
  as the mass of a 12C atom.
• The atomic mass unit scale allows us to use a
  chemical formula to determine the percentage
  composition by mass of a compound.
• 1 amu 1.66054 x 10-24 g and 1g 6.022 x 1023
  amu

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Average Atomic mass
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Weights and Mass

• Questions
• Why is the term weight the proper tem to use?
• Whats the difference between Formula Weights and
  Molecular Weights?

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Empirical and Molecular Weights
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Mass

• Occasionally, we must calculate the percentage
  composition of a compound
• For example, in order to verify the purity of the
  compound, we may wish to compare the calculated
  composition of a substance with that found
  experimentally.

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The Mole
Section 3.4

• Just as a baker uses "dozen" to mean twelve, a
  chemist uses "mole" (abbreviated  mol) to mean
  6.022 x 1023.
• Further, just as the word dozen can apply to any
  collection of twelve objects, the word mole can
  apply to any collection of 6.022 x 1023 objects,
  whether they be atoms, molecules, or ions.

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Conversions

• Conversions between mass, Moles and Numbers of
  particles

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Practice problem 1

• Calculate the number of C atoms in 0.350 mol of
  C6H12O6

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Practice problem 2

• Calculate the mass, in grams, of 0.765 moles of
  Sodium Nitrate.

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Empirical Formulas from Analysis
Section 3.5

• Whats the difference between an Empirical
  Formula and a Molecular Formula?

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Practice problem 3

• A 5.325 g sample of methyl benzoate, a compound
  used in the manufacture of perfumes, is found to
  contain 3.758 g of carbon, 0.316 g of hydrogen,
  and 1.251 g of oxygen. What is the empirical
  formula of the substance?