This document discusses balancing chemical equations. It explains that a chemical equation uses symbols and formulas to represent a chemical reaction and must obey the law of conservation of mass. This law states that the number and type of atoms on the reactants side must equal the number and type on the products side. The document shows an example of an unbalanced equation and uses coefficients to balance the atoms, resulting in an equation that follows the law of conservation of mass.

1. Balancing
Chemical
Equations
TEKS 8.5D recognize that chemical formulas are used to identify substances
and determine the number of atoms of each element in chemical formulas
containing subscripts
TEKS 8.5F recognize whether a chemical equation containing coefficients is
balanced or not and how that relates to the law of conservation of mass

2. occurs when the
chemical bonds
between elements
are formed or
broken.
A chemical reaction

3. This requires
a gain or loss
of energy.

4. is a short, simple
way to describe a
chemical reactions
using symbols and
formulas instead of
words.
A chemical equation

5. are the substances
you begin with in a
chemical reaction.
Reactants

6. These are shown to the
left side of an arrow
called the yield sign.
Fe + 2 HCl FeCl2 + H2
reactants products
yield
sign

7. During a chemical reaction,
the atoms rearrange to form
new bonds between atoms.

8. Products
are the substances you
end with in a chemical
reaction.

9. Products are shown to
the right of the yield
sign arrow.
Fe + 2 HCl FeCl2 + H2
reactants products
yield
sign

10. The products formed in a
chemical reaction have
different properties from the
reactants.

11. A yield sign
Fe + 2 HCl FeCl 2 + H 2
is used to show the
direction of the
chemical reaction.

12. A chemical equation is read
like this:
1 atom
of iron
reacts
with
2 molecules
of
hydrochloric
acid
to yield
1
molecule
of Iron
chloride
and
1
molecule
of
hydrogen
Fe + 2 HCl FeCl2 + H2

13. During a chemical reaction, atoms
cannot be created or destroyed,
so the number of atoms at the
beginning of a reaction MUST
equal the number at the end of
the reaction!

14. This is called the Law of
Conservation of Mass.

15. This law also means that
the mass of the reactants
must equal the mass of the
products.

16. What if the number of
atoms in the reactants
does not match the
number in the products?

17. C3H8 + O2 CO2 + H2O
mass =76 gramsmass =76 grams mass = 62 gramsmass = 62 grams
3-carbon3-carbon 1-carbon1-carbon
8-hydrogen8-hydrogen 2-hydrogen2-hydrogen
2-oxygen2-oxygen 3-oxygen3-oxygen

18. The Law of Conservation of Mass
says that the number of each
atom must be equal on both
sides of the yield sign along
with the masses. Let’s balance
the equation using some basic
rules.

19. Basic Rules for
Balanced
Equations

20. Chemical
formulas
CANNOT be
altered!

21. When balancing an
equation, the subscript
cannot be changed.
H2O
Don’t
change me!

22. Coefficients can be
added before an
element or
molecule.

23. C3H8 + O2 => CO2 + H2O5 3 4
Add coefficients to
the equation to
balance the number of
atoms

24. C3H8 + 5O2 => 3CO2 + 4H2O
3-carbon 3-carbon
8-hydrogen 8-
hydrogen
10-oxygen 10-
oxygen
Atoms on
each side are
equal!!

25. Coefficients were used
to balance the number
of atoms on each side
of the chemical
equation.

26. If we mass the reactants
and products before and
after the reaction, the
masses are equal. We have
followed the law!
mass = 204 grams =>mass = 204 grams
C3H8 + 5O2 => 3CO2 + 4H2O