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Notes chemical equations
1. 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
Balancing
Chemical
Equations
9. Products are shown to
the right of the yield
sign arrow.
Fe
+
2 HCl
reactants
FeCl2
yield
sign
+
products
H2
10. The products formed in a
chemical reaction have
different properties from the
reactants.
11. A yield sign
is used to show the
direction of the
chemical reaction.
Fe + 2 HCl
FeCl 2 + H 2
12. A chemical equation is read
like this:
Fe +
1 atom
of iron
2 HCl
2 molecules
reacts
of
with hydrochloric
acid
FeCl2 +
to yield
1
molecule
of Iron
chloride
H2
1
and
molecule
of
hydrogen
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!
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
mass =76 grams
3-carbon
8-hydrogen
2-oxygen
CO2
+
H2O
mass = 62 grams
1-carbon
2-hydrogen
3-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.
26. C3H8 + 5O2 => 3CO2 + 4H2O
mass = 204 grams =>mass = 204 grams
If we mass the reactants
and products before and
after the reaction, the
masses are equal. We have
followed the law!