Balancing Chemical Equations
Learning Goals:
I will understand…
❏
...what it means to balance
❏
...how to count different elements
in an equation
❏
...how to change the coefficients
to make an equation balanced
Take Note!
We can change the coefficients but
NOT the subscripts!
Balancing Chemical Reactions
To Balance means to make
the same on both sides:
When there is more on one side
than the other, we call this
unbalanced.
5 + __ = 7 + 4
11 = 11
Balancing Chemical Reactions
2
2Mg + O2 → ___MgO
2 2
→
2 2
When this happens in chemistry we
are using atoms and the atoms will
be the same on both sides.
In this example we react:
2 elements to make a compound.
Balancing Chemical Reactions
2 Na and 2 Cl make 2 Na and 2Cl.
2 NaCl
2Na + Cl2 → __
2 2
→
2 2
The atoms have to be
balanced on both sides.
In chemistry we do not
make something new
from nothing.
Balancing Chemical Reactions
2 H2 + O2 → __
2 H2O
4 2
2
→
4 2
2
1
This is called the:
Law of Conservation of Mass
Rules:
1) count each side
2) change one element at a
time
3) Do NOT change subscripts!
4) make the number the same
Balancing Chemical Reactions
YOU TRY!
N2 + 2 O2 → 2__NO2
2
+
2
4
→
1 2
2
4
= 2 and 4
Balanced !
2 and 4
Rules:
1) count each side
2) change one element at a
time
3) Do NOT change subscripts!
4) make the number the same
on both sides for each element
Law of Conservation of Mass
When the Number of each Element is the same on both
sides of an equation, so is the mass.
If the left side weighs 3 grams, how
much does the right side weigh?
Right side = 3 grams
Left = 3 grams
Right = _____
Balancing Chemical Reactions
2nd Try...
C + 2 H2 → __CH4
1
+
2
4
→
1 4
= Right Side
Balanced !
Left Side
Rules:
1) count each side
2) change one element at a time
3) Do NOT change subscripts!
4) make the number the same
on both sides for each element
Balancing Chemical Reactions
3rd Try...
N2 + 3 H2 → 2
__NH3
2
+
2
6
→
1 3
2
6
= 2 and 6
Balanced !
2 and 6
Rules:
1) count each side
2) change one element at a time
3) Do NOT change subscripts!
4) make the number the same
on both sides for each element
Balancing Chemical Reactions
4th Try...
__CO2
2 C O + O2 → 2
11
2
2
2 +
+
4
2→ 2
1 2
4
=
2+4
Balanced !
Rules:
1) count each side
2) change one element at a time
3) Do NOT change subscripts!
4) make the number the same
on both sides for each element
Practice Online
1) Phet Sim. https://phet.colorado.edu/en/simulation/balancing-chemicalequations
N2 + H2 → NH3
H2O → H2 + O2
CH4 + O2 → CO2 + H2O
1) 3 levels (choose from 5 - 15 questions for each)
https://education.jlab.org/elementbalancing/index.html