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Chemical equations 11

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  • 1. Chemical Equations
    • Putting chemical changes into words
  • 2.
    • When atoms are joined together, they form a
    • _____BOND______.
    • Atoms bond together for a very simple reason: atoms like to have full valence shells . (8 electrons)
    • Atoms will share, give away, or gain electrons when forming a bond.
    • Substances in which 2 or more elements have bonded together form a material with unique chemical properties.
    • Example : water - 2 Hydrogen atoms bonded to 1 Oxygen atom. H2O
  • 3. All matter is made of atoms. Why would an atom combine with other atoms? To make the atom stable When an atom combines with another atom, this forms a molecule? The other type of bond is a compound.
  • 4. Compound Molecules
    • A combination of two or more different elements (atoms)
    • Examples:
      • 1 Na atom + 1 Cl atom = the compound NaCl
      • 2 H atoms + 1 O atom = the compound H O
    • The examples above are compounds because the molecule is made out of different atoms.
    2
  • 5. A chemical equation is a symbolic representation of a chemical reaction .
  • 6. Equation Example : The burning of methane gas in oxygen is: CH 4 + 2 O 2 -> CO 2 + 2 H 2 O
  • 7. Review: Element Symbols
    • All elements are represented by a 1 or 2 letter symbol
      • For example
        • C = Carbon
        • Ne = Neon
        • O = Oxygen
    • The symbols are shown on the periodic table
  • 8. Chemical Formulas
    • Shows the elements & number of atoms of each element in a molecule
    • H 2 SO 4
      • Elements
        • Hydrogen; 2 atoms
        • Sulfur: 1 atom
        • Oxygen: 4 atoms
      • 7 atoms total
      • subscripts show the number of atoms of that particular symbol only (the symbol to its left)
    Subscript
  • 9. Coefficients
    • A formula may begin with a number.
    • If there is no number, then “1” is understood to be in front of the formula.
      • This number is called the coefficient .
      • The coefficient represents the number of molecules of that compound or atom needed in the reaction.
      • For example:
        • 2H 2 SO 4 – 2 molecules of Sulfuric Acid
  • 10. Coefficients
    • 2H 2 SO 4 – 2 molecules of Sulfuric Acid
      • A coefficient is distributed to ALL elements in a compound
        • 2 – H 2 (for a total of 4 H atoms)
        • 2 – S (for a total of 2 S atoms)
        • 2 – O 4 (for a total of 8 O atoms)
  • 11. Reading Chemical Equations
    • Each side of an equation represents a combination of chemicals.
    • The combination is written as a set of chemical formulas, separated by + symbols.
      • CH 4 + 2 O 2 -> CO 2 + 2 H 2 O
    Coefficient
  • 12. Reading Chemical Equations
    • The two sides of the equation are separated by an arrow.
      • The combination of chemicals before the reaction are on the left side of the arrow called reactants
      • The right side indicates the combination of chemicals after the reaction called products.
  • 13. For Example :
    • In this reaction, sodium ( Na ) and oxygen ( O 2 ) react to make a single molecule, Na 2 O Label the reactants and products.
    Na + O 2 -> Na 2 O
  • 14. Balancing Equations
    • The Law of Conservation of Mass states that in a chemical reaction, the quantity or amount of each element does not change .
    • This means that each side of the equation must represent the same quantity of each element ; in other words have the same number of each kind of atom.
  • 15. Balancing Equations Na + O 2 -> Na 2 O
    • In order for this equation to be balanced , there must be equal amount of Na on the left hand side and on the right hand side. Right now, there is 1 Na atom on the left but 2 Na atoms on the right.

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