PASTE INTO PAGE 58 OF YOUR NOTEBOOK - PASTE INTO PAGE 58 OF YOUR NOTEBOOK
Name_____________________________________________
North Shore Chemistry
Period: ______________
Date: _______________
58
33
Chemical Equations: Balancing and Translating
Reading adapted from Sarquis’s Modern Chemistry
Introduction
A chemical reaction is the process by which one or more substances are changed into one or
more different substances. In any chemical reaction, the original substances are known as the
reactants, and the resulting substances are known as the products. According to the Law of
Conservation of Mass, the total mass of reactants must equal the total mass of the
products for any given chemical reaction.
Chemical reactions are described by chemical equations. A chemical equation represents
with symbols and formulas, the identities and relative molecular amounts of the
reactants and products in a chemical reaction. For example, the following chemical
equation shows the chemical reaction that happens when Alka-Seltzer tablets are dissolved in
water: citric acid combines with sodium hydrogen carbonate (baking soda) to produce water,
carbon dioxide, and sodium citrate.
H3C6H5O7 + 3 NaHCO3 → 3 H2O + 3 CO2 + Na3C6H5O7
Balancing Equations
Atoms are neither created nor destroyed in ordinary chemical reactions. Thus,
 the same elements are found on both the reactant and product sides of a chemical
equation,
 the atoms of these elements are only rearranged through the breakage of bonds in
reactants and making of new bonds in products when a chemical reaction takes place, and
 the same number of atoms of each element must appear on each side of a
correct chemical equation.
To balance number of atoms, add coefficients where necessary. A coefficient is a small whole
number that appears in front of a formula in a chemical equation. Placing a coefficient in
front of a formula specifies the relative number of molecules of a substance. If no coefficient is
written, it’s assumed to be 1.
*KEY IDEA: It is important to note that the only way to balance a chemical equation is to
change the coefficients of the equation—not the subscripts of a chemical formula. For example, if
we wanted to find a way for water, H2O, to supply 2 atoms of oxygen, we would have to put a 2
as a coefficient, as in 2 H2O. If we changed the subscript of oxygen in water to reflect 2 oxygen
atoms, as in H2O2, this gives us a chemical entirely different from water. H2O2 is actually
hydrogen peroxide, a chemical applied to externally to cuts to prevent bacterial infection.
Balancing Equations Using the “Chain Method”
Step 1: The arrow goes between the reactants and products and acts like an equal sign. Draw a
line where the arrow is to indicate that whatever’s on the left must equal whatever’s on the
right.
Reactants
Products
Cu
+ AgNO3
 Ag
+ Cu(NO3)2
Step 2: Draw out what each compound looks like by “chaining” the atoms/ions together.
Remember that polyatomic ions act as a unit—they never come apart! Notice that there may not
be the same number of atoms of each element.
Reactants
Products
Cu
Cu
+ AgNO3
Ag-NO3
 Ag
Ag
+ Cu(NO3)2
Cu-NO3-NO3
Step 3: Pick an element/polyatomic to balance. It usually helps to balance metals first, then
nonmetals or polyatomic ions. Add more of the element/polyatomic that you want to balance on
the side that has less of it. Remember that elements/polyatomics must be chained to whatever
they are bonded with.
Reactants
Products
Cu
Cu
+ AgNO3
Ag-NO3
Ag-NO3
 Ag
Ag
+ Cu(NO3)2
Cu-NO3-NO3
Step 4: Repeat step 3 with all elements/polyatomic ions until everything is balanced between
the left and right sides.
Reactants
Products
Cu
Cu
+ AgNO3
Ag-NO3
Ag-NO3
 Ag
Ag
Ag
+ Cu(NO3)2
Cu-NO3-NO3
Step 5: Count how many compounds you drew. These will be the coefficients to your equation.
Reactants
Products
1 Cu
1
Cu
+
2 AgNO3
Ag-NO3
2 Ag-NO3
1

2 Ag
Ag
2 Ag
1
+
1 Cu(NO3)2
1
Cu-NO3-NO3
Directions: Follow along with the video, and balance the following examples using the Chain
Method.
Example 1) _____ Ca
+ _____ Pb (NO3)2 → _____ Pb+_____ Ca(NO3)2
Example 2) _____ K
+ _____N2
→ _____K3N
Example 3) _____ AlCl3 + _____ H2SO4
→ ____ Al2(SO4)3+_____ HCl
Example 4) _____ NaOH + _____ HCl
→ _____ NaCl+_____ H2O
Example 5) _____ H2O
→ _____ H2+_____ O2
Tricks and Tips for Balancing Chemical Equations
Hint 1
● # atoms on reactant side = # atoms on products (ALWAYS!!)
● Look for atoms that are not equal on both sides
Hint 2
● Balance metals first.
Hint 3
● Balance nonmetals next.
Hint 4
● Whenever possible, balance by groups (keep polyatomic ions
TOGETHER!!!) instead of by individual elements.
o Ex: 3 Ca(NO3)2 + 2 H3PO4 → Ca3(PO4)2 + 6 HNO3
 Balance the NO3 group and then the PO4 group
Hint 5
● Balance hydrogen (not in a polyatomic) next.
Hint 6
● Balance oxygen (not in a polyatomic) last.
Hint 7
● If you go from one side of the equation to the other and your numbers
just keep going up…
o You’re doing it wrong!
o Erase it and start again.
Balancing Equation Tutorial
●
Independent Practice: Balancing Chemical Equations
Directions: Follow the Law of Conservation of Mass and balance the following
equations. You may work independently or use your peers for help. The answer key will
be posted on Moodle.
1) _____ NaBr
→ _____ Na
+
_____ Br2
2) _____ Zn
+
_____ Sn(NO3)4 → _____ Zn(NO3)2
+
_____ Sn
3) _____ Br2
+
_____ CuF
→ _____ CuBr
+
_____ F2
4) _____ KBr
+
_____ Pb(NO3)2 → _____ KNO3
+
_____ PbBr2
_____ CaCl2
+
_____ NaCl
5) _____ Na2CO3 +
→ _____ CaCO3
6) _____ Na3PO4
+
_____ BaCl2
→ _____ Ba3(PO4)2
+
_____ NaCl
7) _____ Mg(OH)2
+
_____ H2SO4
→ _____ MgSO4
+
_____ H2O
8) _____ LiCl
+
_____ (NH4)2CO3 → _____ NH4Cl
9) _____ NH4OH
+
_____ CrCl3
→ _____ NH4Cl
_____ Al2(SO4)3 +
_____ BaCl2
→ _____ BaSO4
10)
+
+
_____ Li2CO3
_____ Cr(OH)3
+
_____ AlCl3
Translating Chemical Equations
Now that you know about chemical equations and how to name compounds, you can put
these two skills together in order to translate chemical equations. But first, let’s review
what the differences between covalent and ionic bonds are.
Directions: Follow along with the video and fill in the following table.
Compounds
Is the first element a metal?
No
Yes
Covalent
(molecular compound)
particle = molecules
Bonding
Nonpolar
Definition
(no true molecule formed)
particle = formula unit
Nomenclature
Polar
Definition
Ionic
Notes
Binary
Ternary
Nomenclature
Nomenclature
Notes
Notes
Directions: Using the graphic organizer on the preceding page, find the IUPAC chemical
name or chemical formula for each of the following compounds and state whether they
are ionic or covalent compounds.
IUPAC Chemical Name
Magnesium oxide
Magnesium hydroxide
Chemical Formula
MgO
Mg(OH)2
AlCl3
CH4
CO2
Carbon tetrahydride
Ionic or Covalent
Ionic
Ionic
Covalent
Lead(II) nitrate
NaNO3
Potassium chloride
Dinitrogen pentoxide
Now, let’s translate the following balanced equation:
1 MgO
+
1 H 2O

1 Mg(OH)2
The coefficients in a balanced chemical equation can represent the number of atoms,
formula units, molecules or moles for a substance.
 For a single element use the term: atom
 For a diatomic element use the term: molecule
 For a molecular compound use the term: molecule
 For a ionic compound use the term: formula unit
Directions: Give a verbal description to each substance using the
guidelines above.
Substance
MgO
H2 O
Mg(OH)2
Verbal Description
1 formula unit of magnesium oxide
1 molecule of dihydrogen monoxide
1 formula unit of magnesium hydroxide
So, the entire chemical equation should read:
“1 formula unit of magnesium oxide reacts with 1 molecule of dihydrogen monoxide to
produce 1 formula unit of magnesium hydroxide.”
Let’s try another equation:
3 Ba
+
2 AlCl3  3 BaCl2
Substance
3 Ba
2AlCl3
3 BaCl2
2 Al
+ 2 Al
Verbal Description
So, the entire chemical equation should read:
____________________________________________________________
____________________________________________________________
____________________________________________________________
Again:
CH4
Substance
CH4
2 O2
CO2
2 H2O
+
2 O2 
CO2
+
2 H 2O
Verbal Description
So, the entire chemical equation should read:
____________________________________________________________
____________________________________________________________
____________________________________________________________
Independent Practice: Putting It All Together
Directions: Balance each equation and then translate it into a word equation.
Reminder: The coefficients represent the number of atoms, formula units, or molecules
for a substance.
 For a single element use the term: atom
 For a diatomic element use the term: molecule
 For a molecular compound use the term: molecule
 For a ionic compound use the term: formula unit
Example:
2 Na
+
Pb(NO3)2

2 NaNO3
+
Pb
The equation is balanced and the coefficients are 2, 1, 2, 1.
2 atoms of Na react with 1 formula unit of lead(II) nitrate to produce 2 formula
units of sodium nitrate and 1 atom of lead.
1.
AlBr3
+
Cl2

AlCl3
+
Br2
___________________________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
2.
Na3PO4
+
CaCl2

Ca3(PO4)2
+
NaCl
___________________________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
3.
KClO3

KCl
+
O2
___________________________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
4.
Al
+
HCl
AlCl3

+
H2
___________________________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
5.
Ca(OH)2 +
H3PO4

H2 O
+
Ca3(PO4)2
___________________________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________