Middle School Review: Balancing Chemical Equations
Balancing a Chemical Equation Pre-lab
Name: ___________
Name: ______________
1. Aria wanted to design a new bouncy-chew toy for his new puppy.
She used this “equation” to build it. The arrow
“after” building her new toys.
a) Did Aria balance her equation?
shows what she had “before” and
Yes
no
not sure
b) Not so fast…Explain your answer to number 1!
I chose ____________ because _________________________________
c) The “before” objects are called reactants. Go back to the picture of the equation
and
circle all of the reactants
, put (R) in the circle(s).
d) The “after” objects are called products. Go back to the picture of the equation
and put
boxa around all products.
2. In the following chemical equation:
Put a (P) in the box(es).
CO2 + H2O
C2H6 + O2
a) List the products: __________________________________________
b) Is this chemical equation balanced?
 Yes, because ________________________________________
 No, because ________________________________________
Start:
1.
Google: PhET Balancing Chemical Equations
2. Click
on the first link
http://phet.colorado.edu/en/simulation/balancing-chemical-equations
http://phet.colorado.edu/en/simulation/balancing-chemical-equations
http://phet.colorado.edu/en/simulation/balancing-chemical-equations
3. Click on the
button.
Explore the simulation. Be sure to click on everything.
4.
5. Try both
a. Talk about how they may be useful in the activity.
b. Fill in the box-
Tell me what the scale and bar charts are helping you do? What is the purpose of these tools?
_________________________________________________________________________
_________________________________________________________________________
Which one does your group prefer and why? ________________________________________
_________________________________________________________________________
6.
Is this equation balanced? Explain. _________________________________
__________________________________________________________________
Change the coefficients in the equation until you get a
!
What does this smiley face mean?
__________________________________________________________________
7.
Is this equation balanced? Explain. _________________________________
__________________________________________________________________
Using the simulation- add coefficients so that the equation is balanced correctly.
______ H2O
+
______ H2
____ O2
8.
Using the simulation- add coefficients so the equation is balanced correctly.
___ CH4 +
___O2
List all reactants:
9.
___ CO2
+
____ H2O
List all products:
__________________
___________________
__________________
___________________
Discuss the maximum (highest number) of ammonia molecules the simulation will
let you make? Draw them:
In the product, ammonia (2NH3), What does the (2) tell you about the equation?
__________________________________________________________________
What does the (3) tell you?_____________________________________________
Teacher check-off/check-in…
Go on to
tab...
How can I balance an equation?
Name: _______________
Why does an equation have to “balance”?
 It tells us how much will be needed to make a given amount of a new substance (like a
recipe!)
 Law of Conservation of Mass.
 The mass (of all atoms) you start with has to equal the mass (all of the atoms)
that you end with (they can be re-arranged)
 The number and kind of atom you start with has to be the same as the number
and kind of atoms at the end.

This is the “balanced” part!!
Getting started…
1. You need to have an equation with all the chemical formulas written for you (the next
time your work with this you will be able to generate your own formulas for the equations!!! But
for now… work with the ones I throw at you!
2. Draw boxes around all the chemical formulas.
**Once you make the box, do not go in there with your pencil or pen…ever!!!.
H2
+
O2
H2O
3. See what you have by making an “inventory” of the atoms present. For example:
H2
+
H
O
2
Not balanced, too
many oxygen atoms
in the reactants
H2O
O2
=
2
H
O
2
1
4. Write numbers in front of each of the boxes until the inventory for each element is the
same on both sides of the arrow.
H2
x2
New:
+ ___
H
2
2
Double
This!
O2
2
O
2
=
H
2
2√
=
4
H2O
O
1
Now these
are out of
“balance
2√
There are two on the
reactants side!! I have to
“double” the oxygen in
this water molecule with
a coefficient– then start
over with my inventory
New:
2√
4√
Balanced equation:
2 H2
=
4√
+
1 O2
2√
2H2O
 Whenever you change a number, make sure to update the inventory - it is like a puzzle!
 When the number and type of atoms on the left equals the number and type on the right,
(your inventory is equal on both sides)- the equation is balanced.
 Tip: I find that making “odd” atoms “even” - multiply the formula by (2)-really helps!
for example: 1 H20 has only one oxygen atom, but 2H20 has two- this makes it easier to
balance out the other atoms – (4 hydrogen) really helps!
Reminder: 1-boxes 2-inventory 3- balance out the “inventory” using coefficients to get common
multiples of atoms 4- double check to see that the reactant atoms balance with the product atoms
1. __ NaCl
Na
1
+ __ BeF2
Cl
1
Be
1
F
2
--> __ NaF
=
Na
1
+ __ BeCl2
Cl
2
Be
1
F
1
Try some on your own:
1. __FeCl3 + __Be3(PO4)2 --> __BeCl2 + __FePO4
2. __AgNO3 + __LiOH --> __AgOH + __LiNO3
3. __Mg + __Mn2O3 --> __MgO + __Mn
Solutions for the practice problems:
1.
2 FeCl3 + 1 Be3(PO4)2 --> 3 BeCl2 + 2 FePO4
2.
1 AgNO3 + 1 LiOH --> 1 AgOH + 1 LiNO3
3. 3 Mg + 1 Mn2O3 --> 3 MgO + 2 Mn