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
Coefficients
• Used to balance equation
• Represent the number of molecules,
formula units, or atoms of the substances.
http://www.youtube.com/watch?v=x9iZq3ZxbO8&feature=related
• Law of Conservation of Mass
– Mass cannot be created or destroyed.
Zn + 2 HCl → ZnCl2 + H2
Episode 604
2 H2 +
O2 → 2 H2O 2
• Cannot add or change subscripts
• Draw boxes
C3H8 + 5 O2 → 3 CO2
C=3
H=8
O = 2 10
+ 4 H2O
C=1 3
H=28
O = 3 7 10
Episode 604
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
Polyatomic Ions?
Cu
+
2 AgNO3
→
Cu(NO3)2 +
Cu = 1
Ag = 1 2
NO3 = 1 2
2 KNO3
→
K=1 2
N=1 2
O=3 6
2
Ag
Cu = 1
Ag = 1 2
NO3 = 2
2
KNO2
+
O2
K=1 2
N=1 2
O=4 6
Episode 604
Hydrogen and oxygen combine to produce water
H + O → H2O
• Reasonable…?
• But, wrong
2 H2 + O2 → 2 H2O
• 7 Diatomic Elements
– Diatomic: two elements
– Hydrogen, nitrogen, oxygen, fluorine,
chlorine, bromine, iodine
Episode 604
CarbonCS
disulfide
reacts with oxygen
O2
2
to produce carbon
and
COdioxide
2
sulfur
dioxide.
SO
2
CS2 + 3 O2 →
CO2 + 2 SO2
C=1
C=1
S=2
S=1 2
O=46
O=2 6
Episode 604