Balancing
Equations
Balancing Equations
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Balancing chemical equations is
necessary so that they obey the law of
conservation of mass.
Remember, in Ch. R, atoms are not
created or destroyed; they are simply
rearranged.
Balanced equation – a chemical
equation in which mass is conserved;
each side of the equation has the same
number of atoms of each elements.
Balancing Equations
1.
Formulas must be correct
before balancing
2.
Goal: to have equal numbers
of each type of atom on both
sides of the equation.
Balancing Equations
3. Balance by using
COEFFICIENTS (numbers) placed
in FRONT of the Formulas. The
coefficient multiplies everything in
the formula.
Balancing Equations
-- Do Not change the formula.
-- Do NOT change subscripts in
the chemical formulas of
substances to balance
equations!!!
Balancing Equations
4. Coefficients represent the number
of particles or moles.
5. Make sure that the coefficients
are the most reduced ratio.
Odd-Even Balancing
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When you end up with an odd
number of an element on one side
and an even number on the other,
solve it by multiplying the things you
balanced so far by 2.
This problem always occurs with
alkanes (CnH2n+2) with even
numbered carbons.
Balancing Combustion Rxns
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Start with the carbons
Then do the hydrogen
Finally, balance the oxygen
Remember it by C, H, O
Polyatomic Ions in balancing
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If the P.A.I. stays the same on both
sides of the equation, consider the
PAI as a unit (one thing), when
counting atoms.
Practice Problems
Write balanced equations for each of the
following:
1. Magnesium metal and water react to
form magnesium hydroxide and
hydrogen gas.
2.
When ethane burns it combines with
oxygen to form carbon dioxide and
water.
Practice Problems
Balance each of the following
equations
Ag 2O  Ag  O2
C6 H 6  O2  CO2  H 2O
Al2O3  C  Al  CO2