Reactants
are the substances
you begin with.
Fe
+
2 HCl
reactants
FeCl2
yield
sign
+
products
H2
Products
are the substances you
end with.
The yield sign points to
the Product.
Fe
+
2 HCl
reactants
FeCl2
yield
sign
+
products
H2
During a chemical reaction,
the atoms rearrange to form
new bonds between atoms.
Reading a chemical equation:
Fe +
1 atom
of iron
2HCl
2 molecules
reacts
of
with hydrochloric
acid
FeCl2 +
to yield
1
molecule
of Iron
chloride
H2
1
and
molecule
of
hydrogen
Law of Conservation of Mass
Mass can neither be created or
destroyed.
Law of Conservation of Mass
Before and after a chemical reaction……
atoms cannot be created or destroyed.
Law of Conservation of Mass
So the number of atoms at the beginning
and end MUST equal.
Law of Conservation of Mass
So the mass at the beginning and end
MUST equal.
What if the number of
atoms in the reactants
does not match the
number in the products?
C3H8 +
O2
mass =76 grams
3-carbon
8-hydrogen
2-oxygen
CO2
+
H2O
mass = 62 grams
1-carbon
2-hydrogen
3-oxygen
It needs to be balanced!
The Law of Conservation of Mass
states that the number of each
atom and masses must be equal
on both sides of the yield sign.
Rules for
Balancing
Equations
Chemical formulas
CANNOT be
changed!
NaCL
Subscripts CANNOT be
changed!
Don’t
change me!
H2O
Coefficients CAN be
added or changed before
an element or molecule.
H
2H
H 20
2H20
Add coefficients to
the equation to
balance the number of
atoms
C3H8 + 5 O2 => 3CO2 + 4H2O
C3H8 + 5O2 => 3CO2 + 4H2O
3-carbon
8-hydrogen
10-oxygen
3-carbon
8-hydrogen
10-oxygen
Now the atoms are equal,
so the mass is equal.
What is used to balance
equations?
Coefficients