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Write & balance rxns
Write & balance rxns
Write & balance rxns
Write & balance rxns
Write & balance rxns
Write & balance rxns
Write & balance rxns
Write & balance rxns
Write & balance rxns
Write & balance rxns
Write & balance rxns
Write & balance rxns
Write & balance rxns
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Write & balance rxns

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  • 1. I. Intro to Reactions Chp 11: Chemical Reactions
  • 2. A.Signs of a Chemical Reaction <ul><li>Evolution of heat and light </li></ul><ul><li>Formation of a gas </li></ul><ul><li>Formation of a precipitate </li></ul><ul><li>Color change </li></ul>
  • 3. B.Law of Conservation of Mass <ul><li>mass is neither created nor destroyed in a chemical reaction </li></ul>4 H 2 O 4 H 2 O 4 g 32 g 36 g <ul><li>total mass stays the same </li></ul><ul><li>atoms can only rearrange </li></ul>
  • 4. C. Chemical Equations <ul><li>A+B  C+D </li></ul>REACTANTS PRODUCTS
  • 5. C. Chemical Equations
  • 6. D. Writing Equations <ul><li>Identify the substances involved. </li></ul><ul><li>Use symbols to show: </li></ul>2H 2 ( g ) + O 2 ( g )  2H 2 O( g ) <ul><ul><li>How many? - coefficient </li></ul></ul><ul><ul><li>Of what? - chemical formula </li></ul></ul><ul><ul><li>In what state? - physical state </li></ul></ul><ul><li>Remember the diatomic elements. </li></ul>
  • 7. D. Writing Equations <ul><li>Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride. </li></ul><ul><li>How many? </li></ul><ul><li>Of what? </li></ul><ul><li>In what state? </li></ul>Al 2 ( s ) + 3 CuCl 2 ( aq )  3 Cu ( s ) + 2 AlCl 3 ( aq )
  • 8. E. Describing Equations <ul><li>Describing Coefficients : </li></ul><ul><ul><li>individual atom = “atom” </li></ul></ul><ul><ul><li>covalent substance = “molecule” </li></ul></ul><ul><ul><li>ionic substance = “unit” </li></ul></ul>3 molecules of carbon dioxide 2 atoms of magnesium 4 units of magnesium oxide 3CO 2  2Mg  4MgO 
  • 9. E. Describing Equations <ul><li>to produce </li></ul><ul><li>How many? </li></ul><ul><li>Of what? </li></ul><ul><li>In what state? </li></ul>Zn( s ) + 2HCl( aq )  ZnCl 2 ( aq ) + H 2 ( g ) One atom of solid zinc reacts with two molecules of aqueous hydrochloric acid one unit of aqueous zinc chloride and one molecule of hydrogen gas.
  • 10. II. Balancing Equations Chp 11: – Chemical Reactions
  • 11. A. Balancing Steps <ul><li>1. Write the unbalanced equation. </li></ul><ul><li>2. Count atoms on each side. </li></ul><ul><li>3. Add coefficients to make #s equal. </li></ul><ul><li>Coefficient  subscript = # of atoms </li></ul><ul><li>4. Reduce coefficients to lowest possible ratio, if necessary. </li></ul><ul><li>5. Double check atom balance!!! </li></ul>
  • 12. B. Helpful Tips <ul><li>Balance one element at a time. </li></ul><ul><li>Update ALL atom counts after adding a coefficient. </li></ul><ul><li>If an element appears more than once per side, balance it last. </li></ul><ul><li>Balance polyatomic ions as single units. </li></ul><ul><ul><li>“1 SO 4 ” instead of “1 S” and “4 O” </li></ul></ul>
  • 13. C. Balancing Example <ul><li>Aluminum and copper(II) chloride react to form copper and aluminum chloride. </li></ul>1 1 1 1 2 3 2  3  6   3 3 3 2 2  2  6 Al + CuCl 2  Cu + AlCl 3 Al Cu Cl

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