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Balancing Equations and Reactions
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Balancing Equations and Reactions

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Transcript

  • 1. Chemical Equations & Reactions
  • 2. Describing a Chemical Reaction
    Indications of a Chemical Reaction
    Evolution of heat, light, and/or sound
    Production of a gas
    Formation of a precipitate
    Color change
  • 3. Chemical Equations
    An expression showing the formulas of the reactants and products in a chemical reaction
    CH4 + O2 CO2 + H2O
    Reactants
    Products
  • 4. Word Equations
    Describes chemical change using the names of the reactants and products.
    CH4 + O2 CO2 + H2O
    methane + oxygen carbon dioxide + water
    Methane reacts with oxygen to produce carbon dioxide and water
  • 5. Symbols Used in Chemical Equations
    Yields or produces – separates products & reactants
    Used to indicate a reversible reaction
    A reactant or product in the solid state or precipitate
    A reactant or product in the liquid state
    A reactant or product in the gaseous state
    A reactant or product in an aqueous solution
    (dissolved in water)
    (s)
    (l)
    (g)
    (aq)
  • 6. Additional Symbols Used in Chemical Equations
    Formation of a gas (product only)
    Formation of a solid/precipitate (product only)
    Temperature at which reaction is carried out
    Reactants are heated
    Use of a catalyst to speed up reaction
    Important information is usually written above arrow
    i.e. pressure or other reaction conditions
    15 oC
    D
    MnO2
    2 atm
  • 7. Balancing Equations
  • 8. Chemical Equations
    4 Al(s) + 3 O2(g) 2 Al2O3(s)
    product
    reactants
    Depict the kind of reactants and products
    and their relative amounts in a reaction.
    The numbers in the front are called
    stoichiometric coefficients.
  • 9. Chemical Equations
    4 Al(s) + 3 O2(g) 2 Al2O3(s)
    4 g Al + 3 g O2 yield 2 g Al2O3
    This equation means:
    4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3
    or
    4 Al moles + 3 O2moles yield 2 moles of Al2O3
    2 mol Al2O3@102g/mol
    4 mol Al@27g/mol
    3 mol O2@32g/mol
    108 g + 96 g = 204 g
  • 10. Chemical Equations
    Because the same atoms are present
    in a reaction at the beginning (reactants)
    and at the end (products), the amount
    of matter in a system does not change.
    The Law of Conservation of Matter
  • 11. Chemical Equations
    Because of the principle of the conservation of matter,
    An equation must be balanced.
    It must have the same number of atoms
    of the same kind on both sides.
  • 12. CH4 + 2 O2 CO2 + 2 H2O
    Reactants Products
    1 C atom 1 C atom
    4 H atoms 4 H atoms
    4 O atoms 4 O atoms
  • 13. Meaning of Chemical Formula
    Chemical
    Symbol Meaning Composition
    H2O One molecule
    of water:
    Two H atoms and one O atom
    2 H2O Two molecules
    of water:
    Four H atoms and two O atoms
    H2O2 One molecule
    of hydrogen
    peroxide:
    Two H atoms and two O atoms
  • 14. Cl
    H
    H
    H
    Cl
    Cl
    Cl
    H
    reactants products
    reactants products
    H
    H
    Cl
    Cl
    Unbalanced and Balanced Equations
    H
    Cl
    Cl
    Cl
    H
    H
    H2 + Cl2 2 HCl
    (balanced)
    (unbalanced)
    H2 + Cl2 HCl
    2
    1
    2
    2
    1
    2
    2
    2

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