This document provides instructions for balancing chemical equations using the law of conservation of mass. It explains that matter is neither created nor destroyed in chemical reactions, it just changes form. Students are taught to write balanced chemical equations showing the same number and type of atoms on both sides of the reaction. Through an example, it demonstrates how to balance equations by adjusting coefficients in front of compounds to match the number of each element in the reactants and products.

1. You only get out what you put in
Write this title in your notebooks

2. Law of conservation of mass
Matter is neither created nor destroyed – it is just
changes form.
For example, if you react hydrochloric acid with
magnesium:
2HCl + 2Mg  H2+ 2MgCl
You mix a liquid and a solid and get a gas a liquid – but
nothing disappeared, it’s just different.
Write the Law of Conservation of Mass in your notebook

3. Reaction equations
Equations are like the recipes you use to cook
They tell you what to put in – Reactants
And what you’ll get out – Products
Write definitions of reactants and products in your
notebook

4. Equations and balancing
Look back at the equation on slide two.
Copy the equation into your notebook
Count the H, Mg, and Cl atoms in the Reactants and the
Products.
Reactants: _____ H, _____ Mg, _____ Cl
Products: _____ H, _____ Mg, _____ Cl

5. Equations and balancing
Look back at the equation on slide two.
Copy the equation into your notebook
Count the H, Mg, and Cl atoms in the Reactants and the
Products.
Reactants: __2__ H, __2__ Mg, __2__ Cl
Products: __2__ H, ___2_ Mg, ___2_ Cl

6. There were the same number of atoms of each element
in the products as the reactants
You only get out what you
put in.

7. Balancing equations
Whenever we write or use an equation in chemistry it
MUST be balanced and obey the law of conservation of
mass
You only get out what you put in.

8. Balancing equations
Some equations are harder to balance than others, use
the following technique and you’ll be fine.
First write the equation BIG – so it goes all the way
across the page.
Balance this equation in your notebook as you watch a
step by step demonstration.

9. ____Cu2O + ____C → ____Cu + ____CO2
Draw a line in front of each compound
This is where you will write the Coefficient that tells
you how many of each substance you have.
Write a definition of Coefficient in your notebook.

10. ____Cu2O + ____C → ____Cu + ____CO2
Draw a line under the arrow so that you divide the area
into two parts, Reactants and Products

11. ____Cu2O + ____C → ____Cu + ____CO2
Cu - Cu -
O- O-
C- C-
List the elements on each side.
List them in the same order

12. ____Cu2O + ____C → ____Cu + ____CO2
Cu - 2 Cu -
O- 1 O-
C- 1 C-
Now count how many of each element there are on each
side.
I’ve done the Reactants – you do the Products.

13. ____Cu2O + ____C → ____Cu + ____CO2
Cu - 2 Cu - 1
O- 1 O- 2
C- 1 C- 1
Compare the numbers.
Is it balanced?
Are the same number of atoms going in as going out?

14. ____Cu2O + ____C → ____Cu + ____CO2
Cu - 2 Cu - 1
O- 1 O- 2
C- 1 C- 1
No there aren’t
There are more copper atoms on the Reactant side than
on the Product side.
We need more copper on the Product side.

15. ____Cu2O + ____C → ____Cu + ____CO2
Cu - 2 Cu - 1
O- 1 O- 2
C- 1 C- 1
Important rule – we can only change the Coefficients –
the number in front of the compound

16. ____Cu2O + ____C → __2_Cu + ____CO2
Cu - 2 Cu - 1 2
O- 1 O- 2
C- 1 C- 1
Now we have to update our element count.
Look again – is the equation balanced?

17. ____Cu2O + ____C → __2_Cu + ____CO2
Cu - 2 Cu - 1 2
O- 1 O- 2
C- 1 C- 1
No it’s not. There is more Oxygen on the Product side
than on the Reactant side.

18. __2_Cu2O + ____C → __2_Cu + ____CO2
Cu - 2 Cu - 1 2
O- 1 O- 2
C- 1 C- 1
We can only change the coefficients.
So the only way to get more O on the reactant side is to
add another Cu2O

19. __2_Cu2O + ____C → __2_Cu + ____CO2
Cu – 2 4 Cu - 1 2
O- 12 O- 2
C- 1 C- 1
Now we update our element count again.
Look again – is the equation balanced?

20. __2_Cu2O + ____C → __2_Cu + ____CO2
Cu – 2 4 Cu - 1 2
O- 12 O- 2
C- 1 C- 1
No it’s not – there is more copper on the Reactant side
than the product side.

21. __2_Cu2O + ____C → __4_Cu + ____CO2
Cu – 2 4 Cu - 1 2
O- 12 O- 2
C- 1 C- 1
We can only change the coefficients.
Change the Cu to 4.

22. __2_Cu2O + ____C → __4_Cu + ____CO2
Cu – 2 4 Cu - 1 2 4
O- 12 O- 2
C- 1 C- 1
Now we update our element count again.
Look again – is the equation balanced?

23. __2_Cu2O + ____C → __4_Cu + ____CO2
Cu – 2 4 Cu - 1 2 4
O- 12 O- 2
C- 1 C- 1
Yes!
It is balanced.
2Cu2O + C  4Cu + CO2

24. Practice
Now it’s your turn.
Follow the steps we just used and balance the following
equations:
1. Write the equation big
2. Draw a line under the arrow
3. List the elements
4. Count the elements – is it balanced?
5. If not, change the Coefficients
6. Count again and repeat from step 4.

25. Practice 1/5
___Na + ___Cl2  ___NaCl

26. Practice 2/5
___H2 + ___O2  ___H2O

27. Practice 3/5
___SnO2 + ___H2  ___Sn + ___H2O

28. Practice 4/5
___NaCl + ___F2  ___NaF + ___Cl2

29. Practice 5/5
___CH4 + ___O2  ___CO2 + ___H2O

30. Balancing polyatomics
Do you remember polyatomic ions?
Ions that have more than one element in them
 SO42+
 NO3 -
 OH-
There’s a shortcut…

31. __H2SO4 +__Zn  __ZnSO4 + __H2
H-2 H-2
S- 1 S- 1
O- 4 O- 4
Zn - 1 Zn - 1
Instead of writing out all of the S and O separately,
notice that SO4 is together on both sides.

32. __H2SO4 +__Zn  __ZnSO4 + __H2
H-2 H-2
SO4 - 1 SO4 - 1
Zn - 1 Zn - 1
We can count the SO4‘s instead.

33. Practice 1/2
__Al2(SO4)3 + __Ca(OH)2 → __Al(OH)3 + __CaSO4

34. Practice 2/2
__AgNO3 + __K3PO4 → __Ag3PO4 + __KNO3

36. The end.