Chemical equations 11


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Chemical equations 11

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