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Counting Atoms and Balancing Chemical Equations

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Subscripts C 12 H 22 O 11 There are 12 atoms of Carbon There are 22 atoms of Hydrogen There are 11 atoms of Oxygen If there is not a subscript listed, it is understood to be 1. NaCl There is one atom of Sodium There is one atom of Chlorine

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Learning Check NaHCO 3 Sodium – 1 Hydrogen – 1 Carbon – 1 Oxygen -3 HCl Hydrogen – 1 Chlorine - 1

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There are times you will see a compound with parenthesis. Pb(NO 3 ) 2 The 2 after the parenthesis indicates there are two sets of the parenthesis. Pb(NO 3 ) (NO 3 ) So, in counting the atoms, you would have the following: Lead – 1 Oxygen – 6 Nitrogen -2

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(NH 4 ) 3 PO 4 Nitrogen – 3 Hydrogen – 12 Phosphorus – 1 Oxygen – 4 Mg(OH) 2 Magnesium – 1 Oxygen – 2 Hydrogen – 2 Learning Check

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2H 2 SO 4 This means there are 2 compounds of sulfuric acid. Think: H 2 SO 4 + H 2 SO 4 Counting the atoms: Hydrogen – 4 Sulfur – 2Oxygen – 8 Coefficient

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3H 3 PO 4 Hydrogen – 9 Phosphorus – 3 Oxygen - 12 2H 2 O Hydrogen – 4 Oxygen - 2 Learning Check

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Reading Chemical Equations The mass of all the reactants (the substances going into a reaction) must equal the mass of the products (the substances produced by the reaction). CH 4 + 2O 2 → CO 2 + 2 H 2 O ReactantsProducts

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Law of Conservation of Mass In a chemical reaction, matter cannot be created or destroyed. It can only be changed. The reactants MUST contain the same elements and the same number of each element as the product. They CAN be in different compounds.

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Do the following equations follow the law of conservation of mass? H 2 + O 2 H 2 O Na + O 2 Na 2 O Mg + 2HCl MgCl 2 + H 2 HgO Hg + O 2 N 2 + 3H 2 2NH 3 2Na + 2H 2 O 2NaOH + H 2 Zn + 2HCl ZnCl 2 + H 2 Learning Check NO YES NO YES

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Na + O 2 → Na 2 O For this equation to be balanced, there must be equal amounts of Na in the reactants and products. You must add coefficients to balance this equation: 2Na + O 2 → Na 2 O Balancing Equations

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Two ways… M. I. N. O. H. or Number charts

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Balancing Equations M. I. N. O. H. Two ways…

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Add coefficients first M - Metals Balance metals such as Fe or Na first.

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Add coefficients first M - Metals Balance metals such as Fe or Na first. Second I - Ions Looks for polyatomic ions (such as PO 4 -3 or SO 4 -2 ) that cross from reactant to product unchanged. Balance polyatomic ions as a group within its parentheses.

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Add coefficients first M - Metals Balance metals such as Fe or Na first. Second I - Ions Looks for polyatomic ions (such as PO 4 -3 or SO 4 -2 ) that cross from reactant to product unchanged. Balance polyatomic ions as a group within its parentheses. Third N - Non-metals Chlorine (Cl) or Sulfur (S) are common non-metals to look for!

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Add coefficients first M - Metals Balance metals such as Fe or Na first. Second I - Ions Looks for polyatomic ions (such as PO 4 -3 or SO 4 -2 ) that cross from reactant to product unchanged. Balance polyatomic ions as a group within its parentheses. Third N - Non-metals Chlorine (Cl) or Sulfur (S) are common non-metals to look for! Fourth O - Oxygen Remember, oxygen by itself is O 2

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Add coefficients first M - Metals Balance metals such as Fe or Na first. Second I - Ions Looks for polyatomic ions (such as PO 4 -3 or SO 4 -2 ) that cross from reactant to product unchanged. Balance polyatomic ions as a group within its parentheses. Third N - Non-metals Chlorine (Cl) or Sulfur (S) are common non-metals to look for! Fourth O - Oxygen Remember, oxygen by itself is O 2 Fifth (last) H - Hydrogen Remember, hydrogen by itself is H 2

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Balancing Equations Two ways… Number charts

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Balancing Equations __H 2 + __O 2 __H 2 O __H 2 + __O 2 __H 2 O O - H - O - H - 2222 1212 2 2424 2 4

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__H 2 SO 4 + __NaOH __H 2 O +__Na 2 SO 4 __H 2 SO 4 + __NaOH __H 2 O +__Na 2 SO 4 Na - SO 4 – O – H - Na - SO 4 – O – H - 11131113 21122112 2 224224 2 2424 Balancing Equations

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__C 3 H 8 + __O 2 __CO 2 +__H 2 O __C 3 H 8 + __O 2 __CO 2 +__H 2 O C - O – H – C - O – H – 328328 132132 3 3737 4 10 8 5 10 Balancing Equations

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