Counting Atoms and Balancing Chemical Equations

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

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

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

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

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

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

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 H 2 O ReactantsProducts

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? 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

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

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

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

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

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.

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!

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

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

Balancing Equations Two ways… Number charts

Balancing Equations __H 2 + __O 2  __H 2 O __H 2 + __O 2  __H 2 O O - H - O - H

__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 Balancing Equations

__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 – Balancing Equations