Transcript How to balance


Everything that goes into a chemical
equation must be accounted for (This is the
law of conservation of mass: Matter cannot
be created or destroyed)

This is also helpful because we can see how
much product (right side of the equation)
that we will get depending on the amount
of reactant (left side) that we put in.

Hydrogen peroxide decomposes into
water and oxygen.

Balance the equation: H2O2  H2O + O2

We cannot change the subscript (the little
numbers) because that would change the
chemical formula and then it would be a
completely different chemical. What we
can do is put a big number in the front of
each compound. The number we put in
the front is called the coefficient. We use
coefficients to balance chemical
equations.

Think of the arrow as an equal sign. You
can go back and forth and make sure
you have the same number of each
element on both sides, or you can use
the chart method to get you started.
H2 O 2  H 2 O + O 2
Reactant
2
H
2
O
Product
2
3
I have 3 Oxygens (O) on the right because the first
one adds to the second two. Use the plus sign to
help you remember to add. My Hydrogens (H)
match, but my Oxygens (O) don’t so I need to fix
them. When I put a coefficient in front it will multiply
everything in the formula.
H2O2  2H2O + O2
I now have:
Reactant
Product
2
H
2 4
2
O
3 4
2H2O2  2H2O + O2
Now I have:
Reactant
Product
4 2
H
2 4
4 2
O
3 4
Make sure that you can’t reduce your
coefficients any more than they already
are. For example: 2Cu + 4AgNO3  4Ag +
2Cu(NO3)2
 I can divide all of the coefficients by 2, so I
should have: Cu + 2AgNO3  2Ag +
Cu(NO3)2

1.
3 H2 +
N2 
Reactants
6 2
2
2NH3
H
N
Products
3 6
1
2
2.
C+
H2O 
Reactants
1
2
1
CO + H2
C
H
O
Products
1
2
1
The equation is already balanced so
you just need to write “balanced”
underneath the equation
3.
AgNO3 + FeCl3 
Reactants
1
Ag
1
N
3
O
1
Fe
3
Cl
AgCl + Fe(NO3)3
Products
1
3 The number outside
the parentheses
9 multiplies what is
1 inside
1
3.
3 AgNO3 + FeCl3  3 AgCl + Fe(NO3)3
Reactants
3 1
3 1
9 3
1
3
Ag
N
O
Fe
Cl
Products
1 3
3
9
1
1 3