5 3 Lecture

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5 3 Lecture

  1. 1. 5.3 Balancing Chemical Equations Pages 161 - 165
  2. 2. Goal 1 Describe and balance chemical equations
  3. 3. <ul><li>Word equation </li></ul>Methane + Oxygen  Carbon dioxide + Water Reactants Products
  4. 4. <ul><li>Chemical Equations </li></ul><ul><ul><li>Balanced to show conservation of mass </li></ul></ul><ul><ul><li>#Atoms per element go in = # Atoms per element that come out </li></ul></ul>Important !!
  5. 5. <ul><li>Chemical equations </li></ul><ul><ul><li>Use chemical formulas and coefficients </li></ul></ul>CH 4 + 2 O 2  CO 2 + 2 H 2 O
  6. 6. <ul><li>Coefficients used to show </li></ul><ul><ul><li># of molecules/compounds </li></ul></ul><ul><ul><li># of moles </li></ul></ul><ul><ul><li>Multiply subscripts by coefficients to determine the # of atoms </li></ul></ul>CH 4 + 2 O 2  CO 2 + 2 H 2 O
  7. 7. <ul><li>C = </li></ul><ul><li>H = </li></ul><ul><li>O = </li></ul><ul><li>C = </li></ul><ul><li>H = </li></ul><ul><li>O = </li></ul>CH 4 + 2 O 2  CO 2 + 2 H 2 O # of atoms on left MUST = # of atoms on right Is this equation balanced?
  8. 8. CH 4 + 2 O 2  CO 2 + 2 H 2 O Yes! It’s balanced
  9. 9. <ul><li>H = </li></ul><ul><li>O = </li></ul><ul><li>H = </li></ul><ul><li>O = </li></ul>H 2 + O 2  H 2 O # of atoms on left MUST = # of atoms on right Is this equation balanced?
  10. 10. <ul><li>Uh-Oh! </li></ul>
  11. 11. <ul><li>H = </li></ul><ul><li>O = </li></ul><ul><li>H = </li></ul><ul><li>O = </li></ul>H 2 + O 2  H 2 O # of atoms on left MUST = # of atoms on right How can we balance it?
  12. 12. <ul><li>Rules for balancing chemical equations </li></ul><ul><ul><li>1. Only change coefficients </li></ul></ul><ul><ul><li>2. Never never never ever change a subscript </li></ul></ul><ul><ul><li>3. Multiply subscripts by coefficients </li></ul></ul><ul><ul><li>4. Compounds FIRST </li></ul></ul><ul><ul><li>5. Elements LAST </li></ul></ul>
  13. 13. <ul><li>H = </li></ul><ul><li>O = </li></ul><ul><li>H = </li></ul><ul><li>O = </li></ul>__ H 2 + __ O 2  __ H 2 O # of atoms on left MUST = # of atoms on right Try it…
  14. 14. <ul><li>H = 4 atoms </li></ul><ul><li>O = 2 atoms </li></ul><ul><li>H = 4 atoms </li></ul><ul><li>O = 2 atoms </li></ul>_ 2 _ H 2 + __ O 2  _ 2 _ H 2 O # of atoms on left MUST = # of atoms on right Try it…
  15. 15. <ul><li>Mg = </li></ul><ul><li>O = </li></ul><ul><li>Mg = </li></ul><ul><li>O = </li></ul>__ Mg + __ O 2  __ MgO # of atoms on left MUST = # of atoms on right Let’s try it again…
  16. 16. <ul><li>Mg = 2 atoms </li></ul><ul><li>O = 2 atoms </li></ul><ul><li>Mg = 2 atoms </li></ul><ul><li>O = 2 atoms </li></ul>_2_ Mg + __ O 2  _2_ MgO # of atoms on left MUST = # of atoms on right How did you do?
  17. 17. <ul><li>C = </li></ul><ul><li>H = </li></ul><ul><li>C = </li></ul><ul><li>H = </li></ul>__ CH 4  __ C 3 H 8 + __ H 2 # of atoms on left MUST = # of atoms on right Let’s try it one more time…
  18. 18. <ul><li>C = </li></ul><ul><li>H = </li></ul><ul><li>C = </li></ul><ul><li>H = </li></ul>_ 3 _ CH 4  __ C 3 H 8 + _ 2 _ H 2 # of atoms on left MUST = # of atoms on right How did you do?
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