Do Now:
1. What is a chemical formula? Give an example.
2. What is a chemical equation?
3. What does the law of conservation of mass/matter say?
AGENDA
1) Do Now
2) Chemical Formula Practice
3) Intro to Balancing Equations
Title: Balancing Equations Standard___
Homework: Chemical Formulas Practice
Chemical Formulas
• We KNOW, a chemical formula is the combination of
elemental symbols that are in a substance,
• … but what are those numbers?
Subscript
• A subscript is the number written below and to the
RIGHT of the chemical symbol.
• It means there are that many of those atoms.
• If there is no subscript, that means only one atom of
the element is there. Ex. NaCl
• “Sub” means “under”. The subscript is UNDER the
chemical symbol!
CO2 Subscript
H2O
MgCl2
Coefficient
• A coefficient is the number placed in FRONT of a
chemical symbol or formula.
• You MULTIPLY the number (subscript) of each
element in the formula by this number.
Subscript
Coefficient
2CO
3H2O
Label the subscript and coefficient:
1. C6H12O6
6. N2CO3
2. 2HCl
7. CaSO4
3. 3NaO2
8. Fe2O3
4. NaHO5
9. 4NaOCl
5. CuS2
10. Al2SO4
Chemical Formulas and Counting Atoms
Practice!
• Work with your table partner to finish the
worksheet front and back.
• This activity is…
• 12 inch voices
• Stay seated!
• Well go through the front side together…
Creating Chemical
Formulas
Once we understand formulas…
• We can look at equations!
Review of Formulas
• 3HCl2
• CH(NaO3)2
• 4NOH2O
• 2Mg2(Cl2O)3
Steps:
1.ID the elements
2.Count up the
subscripts
3.Get rid of the
parentheses
4.Distribute the
coefficient
Chemical Equations
• Chemical equations are used to describe reactions.
• A chemical equation uses chemical formulas and symbols
as a short way to describe a chemical reaction.
• Ex. C + O2  CO2
• H + O  H 2O
• Finish this chemical equation: Na + Cl  ______
Balancing equations
• The Law of Conservation of Matter (Mass tells us that
the mass of the reactants that we start with, HAS TO BE
the same as the products that we end with.)
• When we write a CHEMICAL EQUATION, we want to
make sure that it follows this law. We call it a “balanced
equation”.
• This means that there is the same number of atoms of
each element on EACH side of the equation (before and
after)
The STEPS of
Balancing Chemical
Equations
Conservation of Matter
• Matter is NEVER created, nor destroyed
• Chemical Reaction
- elements and total # of atoms in the
reactants must be the same for products
reactant
# of atoms
before the
reaction
product
=
# of
atoms
after the
reaction
Knowing this, lets
look back at that
anticipation guide
from last week…
Reactant  Product
Before the reaction = after the reaction
H2 + O2  H2O
What are the reactants?
What are the products?
What elements are present on both sides?
Is the equation balanced (equal)?
Why?
How can the number of atoms on both sides of
the equation be balanced?
1. Identify all the elements
involved in the reaction:
H2 + O2 --> H2O
H
O
2. Count the number of atoms
(use subscripts) of EACH
element on BOTH sides:
H2 + O2 --> H2O
reactants
2 -H- 2
2 -O- 1
product
3. Identify which side needs more atoms.
Put COEFFICIENTS, MULTIPLY and
RECOUNT the atoms. Do not change the
formula.
H2 + O2 --> 2 H2O
2 -H- 2 4
2 -O- 1 2
4. Do the same (C,M,R) on the
other side until ALL the atoms on
both sides are EQUAL.
2 H2 + O2 --> 2 H2O
4 2 -H- 2 4
2 -O- 1 2
EXERCISE: BALANCE THE
EQUATION. FOLLOW THE
STEPS.
H2 +
Cl2
--->
HCl2
2.
KClO3 -->
KCl +
O2
Practice together:
1.
CaO  Ca + O
2.
N 2 + H2 
NH3
3. Al2(SO4)3+ NaF→ Al F3 + Na2SO4
- Al -S-O-
- Na -F-
Now try it on your own!
• This activity is:
• Independent
• You are:
• In your seat
• Working with your partner if you need
help
• Using 12 inch voices
Homework
Finish the worksheet
on balancing
equations! 