1. Chemical Equation
A shorthand way of reporting details of a chemical reaction
Reactants
The starting substances in a reaction
Placed on the left side of the equation
Products
The substances formed during a chemical reaction
Placed on the right side of the equation
Arrow is read as yields
Episode 604

2. Coefficients 2 Used to balance equation
Represent the number of molecules, formula units, or atoms of the substances.
Law of Conservation of Mass
Mass cannot be created or destroyed.
Zn + HCl → ZnCl H2 2
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3. Cannot add or change subscripts
H O2 → H2O
Cannot add or change subscripts
Draw boxes
C3H O2 → CO H2O 2 2 2 5 3 4
C = 3
C = 1 3
H = 8
H = 2 8
O = 2 10
O = 3 7 10
Episode 604

4. Guidelines for Balancing Equations
Start by making an element inventory
Draw boxes around each formula in the equation
Begin with one molecule or formula unit of the substance containing the most atoms
Balance polyatomic ions that appear on both sides of the equation as a single unit
Appears in a reactant and a product
Balance hydrogen and oxygen atoms last
Episode 604

5. Cu + AgNO3 → Cu(NO3)2 + Ag KNO3 → KNO2 + O2
Polyatomic Ions? 2 2
Cu + AgNO3 → Cu(NO3)2 + Ag KNO3 → KNO2 + O2
Cu = 1
Cu = 1
Ag = 1 2
Ag = 1 2
NO3 = 1 2
NO3 = 2 2 2 2
K = 1 2
K = 1
N = 1 2
N = 1 2
O = 3 6
O = 4 6
Episode 604

6. Hydrogen and oxygen combine to produce water
H O → H2O
Reasonable…?
But, wrong
H2 + O2 → H2O
7 Diatomic Elements
Diatomic: two elements
Hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, iodine
Balance it ! 2 2
Episode 604

7. CS2
Carbon disulfide reacts with oxygen to produce carbon dioxide and sulfur dioxide. O2
CO2
SO2
Balance it !
CS2 + O2 → CO2 + SO2 3 2
C = 1
C = 1
S = 2
S = 1 2
O = 2 6
O = 4 6
Episode 604