Name:
Date:
5.4
Topic: Balancing Chemical Equations
Learning Objectives:
1. I can explain why a chemical equation needs to be balanced according to the Law of Conservation of
Mass
2. I can balance a chemical equation
3. I can determine the molar ratio between two chemicals from a balanced chemical equation
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Bellringer
1. What is the Law of Conservation of Mass?
2. For the chemical reaction below, fill in the missing mass:
LiCl + MgS  Li2S + MgCl2
7g + 3g
 4g
+ ____g
3. What does the word “accountability” mean to you:
Week of 11/11-11/15: ACTION PLAN
What is my current average in this class (Look at your character report card): _____________
Am I missing any assignments/tests in this class? (Am I missing the Unit 4 Test?) _____________
OR… Am I planning on RETAKING the Unit 4 Test? _______________
If your answer was yes to either… WHEN do you plan on retaking the test? (Check one):
☐
Other ☐ : __________________________________________
Thursday at Lunch
Have I been ABSENT for any days of this class during this unit?
 5.1: Physical and Chemical Changes (Tues) : __________ (yes or no)
 5.2: Types of Reactions (Thurs) : ___________ (yes or no)
If your answer was yes… What is your plan for catching up? (Check one):
Get the notes online
☐
Come to the review session on Thursday ☐
On a scale from 1 to 5, how comfortable am I with the material in this unit (5 = I understand
everything, 1 = I have no idea what is going on) CIRCLE ONE
1
2
3
4
5
If your answer was 3 or less, how do you plan to review the material before the test?
Take notes home to study
☐
Come to the review session on Thursday ☐
This week’s action Items:
What do I need to do?
When do I need to do it?
How will I remind myself?
Notes:
KP 1: What does the Law of Conservation of Mass say?
 Matter can neither be created or destroyed
 Every element has to have the same number of ____________ on the left (reactants) side and
right (products) side of a chemical equation. When this is true, the chemical equation is
“__________________”
 Example:
o NOT Balanced, cannot occur in nature: N2 + O2  NO2
(N atoms appear to be
destroyed)
o Balanced, can occur in nature: N2 + 2O2  2NO2
(N atoms and O atoms are
conserved)
o If you have ___ Nitrogens on the left side, you have to have ____ Nitrogens on the right
side because Nitrogen atoms can neither be created nor destroyed in a chemical reaction!
KP 2: How do I count atoms?
 #Atoms = Coefficient x Subscript
o Coefficient =Big Number in front (applies to the WHOLE compound!)
o Subscript = Little Number on bottom right (applies only to the element before it)
o No number means “1”

Example #1: 2SO3
o There are 2 Sulfur atoms because 2x1=2
o There are 6 Oxygen atoms because 2x3=6

Example #2: Li3N
o There are ____ Lithium atoms because _____________
o There is _____Nitrogen atom because ______________

Example #3: 4C2H3O2
o There are ______ Carbon atoms because _____________
o There are ______ Hydrogen atoms because _____________
o There are _______Oxygen atoms because ______________
Practice Counting Atoms
1. NaOH
Na: ____
H:_____
O: ____
2. 3CH4
3. 6H2S
C: ____
H: ____
H:____
S: ______
4. Mg2SO4
______
Mg: ____
S: _____
O:
5. 2SO3
S: _____
O:________
KP 3: How can I balance a chemical equation?
1. BOX: Draw ___________ around each chemical formula
2. COUNT: Write how many atoms of each element are on the _______ and ____________
COEFFICIENT: Pick one __________________ element to start with. On the side that has
LESS, put a BIG number to make both sides equal. Continue until all elements are balanced!
3. Leave ________________ and _______________ for last!
4. NEVER change anything in the boxes…just add coefficients!
Examples of Balancing Chemical Equations:
1. _____ H2 + _____ O2  _____ H2O
4. __CH4 + __O2  __CO2 +__H2O
2.
_____ N2 +_____ H2 _____ NH3
5.
_____ N2 + _____ O2  _____ N2O
3.
_____ S8 + _____ O2  _____ SO3
6.
_____ HgO  _____ Hg + _____ O2
Key Point 4: How do I determine the molar ratio between two chemicals?
 The molar ratio is the ratio (______________) of the _______________________ between 2
chemicals in a balanced chemical equation
 To find the molar ratio between 2 chemicals, first balance the equation, and then write the
coefficients for the chemicals as a ratio or fraction
 Example: 4NH3 + 5O2  4NO + 6H2O
1) What is the molar ratio between NH3 and NO? _________
2) What is the molar ratio between NH3 and H2O? __________
3) What is the molar ratio between O2 and NO? ___________
4) What is the molar ratio between O2 and H2O? ___________
Independent Practice:
Macro (BIG)
Explain why all chemical
equations must be balanced.
Nano (small)
Symbolic
NO2 + 2Li2Se  NSe2 + 2Li2O
Using the equation above, what is
the correct molar ratio between
NO2 and NeS2?
C + H2  CH4
Explain why this chemical
equation can never occur
(Hint: look back at Key
Point #1)
What is the correct molar ratio
between Li2Se and Li2O?
What is the correct molar ratio
between NO2 and Li2O?
Balance the following equations so that they follow the Law of Conservation of Mass.
1) ___Li + ___CuCl2  ___LiCl + ___Cu
2) ___Fe + ___S8  ___FeS
3) ___C3H8 + ___O2  ___H2O + ___CO2
4) ___Al + ___O2  ___Al2O3
Explain how you know that the following chemical equation could not occur.
Be + Cl2  Be2Cl3
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________________________________________________________________________________
Which of the following equations best illustrates the Law of Conservation of Mass? Why?
1) C2H3 + O2  CO2 + H2O
2) 2Li + MgF2  2LiF + Mg
3) Ca + F2  2CaF2
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Use the following equation to answer the questions below: Be + F2  Be2F3
a. What is wrong with the equation?
b. Fix the equation by writing it correctly in the space below.