Counting Atoms and Balancing Chemical Equations

If there is not a subscript listed, it is understood to be 1. Subscripts C12H22O11 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

Learning Check NaHCO3 HCl Sodium – 1 Hydrogen – 1 Carbon – 1 Oxygen -3 Chlorine - 1

There are times you will see a compound with parenthesis. Pb(NO3)2 The 2 after the parenthesis indicates there are two sets of the parenthesis. Pb(NO3) (NO3) So, in counting the atoms, you would have the following: Lead – 1 Oxygen – 6 Nitrogen -2

Learning Check (NH4)3PO4 Mg(OH)2 Nitrogen – 3 Magnesium – 1 Hydrogen – 12 Phosphorus – 1 Oxygen – 4 Mg(OH)2 Magnesium – 1 Oxygen – 2 Hydrogen – 2

Hydrogen – 4 Sulfur – 2 Oxygen – 8 Coefficient 2H2SO4 This means there are 2 compounds of sulfuric acid. Think: H2SO4 + H2SO4 Counting the atoms: Hydrogen – 4 Sulfur – 2 Oxygen – 8 Coefficient

Learning Check 3H3PO4 2H2O Hydrogen – 9 Hydrogen – 4 Phosphorus – 3 Oxygen - 12 2H2O Hydrogen – 4 Oxygen - 2

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). CH4 + 2O2 → CO2 + 2 H2O Reactants Products

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.

Do the following equations follow the law of conservation of mass? Learning Check Do the following equations follow the law of conservation of mass? H2 + O2 H2O Na + O2 Na2O Mg + 2HCl MgCl2 + H2 HgO Hg + O2 N2 + 3H2 2NH3 2Na + 2H2O 2NaOH + H2 Zn + 2HCl ZnCl2 + H2 NO YES

You must add coefficients to balance this equation: Balancing Equations Na + O2 → Na2O 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 + O2 → Na2O

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

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

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

M - Metals I - Ions Add coefficients first Balance metals such as Fe or Na first. Second I - Ions Looks for polyatomic ions (such as PO4-3 or SO4-2) that cross from reactant to product unchanged. Balance polyatomic ions as a group within its parentheses.

M - Metals I - Ions N - Non-metals Add coefficients first Balance metals such as Fe or Na first. Second I - Ions Looks for polyatomic ions (such as PO4-3 or SO4-2) 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!

M - Metals I - Ions N - Non-metals O - Oxygen Add coefficients first Balance metals such as Fe or Na first. Second I - Ions Looks for polyatomic ions (such as PO4-3 or SO4-2) 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 O2

M - Metals I - Ions N - Non-metals O - Oxygen H - Hydrogen Add coefficients first M - Metals Balance metals such as Fe or Na first. Second I - Ions Looks for polyatomic ions (such as PO4-3 or SO4-2) 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 O2 Fifth (last) H - Hydrogen Remember, hydrogen by itself is H2

Balancing Equations Two ways… Number charts

Balancing Equations __H2 + __O2  __H2O 2 2 O - H - 2 4 O - H - 1 2 2

Balancing Equations __H2SO4 + __NaOH  __H2O +__Na2SO4 2 2 Na - SO4 – 1 3 2 4 Na - SO4 – O – H - 2 1 2 4

Balancing Equations __C3H8 + __O2  __CO2 +__H2O 5 3 4 C - O – H – 3 2 10 C - O – H – 1 3 2 3 7 10 8