Topic: Stoichiometry: Balancing
Chemical Equations
What is stoichiometry?
• The study of quantitative relationships in a
balanced chemical equation
• Balance equations represent chemical
reactions
– Remember in chemical reactions 3 things are
conserved
• Matter
• Energy
• charge
Law of Conservation of Matter
• Matter is neither created nor destroyed
in a chemical reaction
• Mass reactants = Mass products
• Chemical bonds in reactants may break
• New bonds may form to produce products
• Number of atoms of each element is
“constant”
• # of atoms of each element is the same on
both sides of the equation
Writing Chemical Equations
Begin with word equation
Solid Tin (IV) Oxide is heated with Hydrogen gas
to form tin metal and water vapor.
Next go to skeleton equation: replace names of
substances with chemical formulas
SnO2(s) + H2(g)  Sn(s) + H2O(g)
Balance skeleton equation: # of atoms of
each element is the same on both sides of the
equation (law of conversation of mass)
- let’s figure out how to balance
Equation Balancing…
let’s RAP
R
A
P
SnO2(s) + H2(g)  Sn(s) + H2O(g)
122-
Sn - 1
O -1
H -2
NOT BALANCED
SnO2(s) + 2 H2(g)  Sn(s) +2 H2O(g)
124 2-
Sn - 1
O -1
H -2
2
4
• Find the most complex compound and then compare the number
of each element on product side and reactant side
• Look at H2O – 2 Hydrogen and 1 oxygen
• On reactant side, 2 Oxygen and 2 Hydrogen
• Use Coefficients to balance the numbers of each atom, check
number of atoms as you go: NOTE: NEVER CHANGE
SUBSCRIPTS
BALANCED 
NOTE: Coefficients must be in lowest possible ratios
2SnO2(s) +
4H2(g) 
2Sn(s) +
4H2O(g)
Fe + O2  Fe2O3
• HINTS:
– Most Complex = Fe2O3
– ODDS ARE AKWARD, so Try to make O3 even!!!!!!!
4Fe + 3O2  2 Fe2O3
AgNO3 + MgCl2  Mg(NO3)2 + AgCl
• HINTS:
– Keep polyatomics together
•
•
•
•
NO3
Ag
Cl
Mg
2 AgNO3 + MgCl2  Mg(NO3)2 + 2 AgCl
Na + H2O  NaOH + H2
• HINTS:
– ODDS ARE AKWARD – try to make even
• H on product side H + H2 = 3 hydrogens
2 Na + 2 H2O  2 NaOH + H2