Balancing Chemical Equations Notes
Balancing Chemical Equations
 To describe a reaction accurately, a chemical equation must show the _________ number
of each type of atom on ______ _______ of the equation.
 Chemists say an equation is balanced when it accurately represents _______________
____ ________.
How to Balance a Chemical Reaction
1. Write the ____________
2. ____________ the atoms
3. Use ___________ to balance atoms
4. Look back and __________
Step 1: Write the Equation
 Write the correct formulas for both the __________ and ______________.
H2
+
O2

H2O
Reactants
Products
 Place the __________, H2 and O2, on the _____ side of the arrow, separated by a plus
sign.
 Next, write the ___________, H2O, on the _______ side of the arrow.
Step 2: Count the Atoms
 Count the number of ________ of each element on _____
H2
+
O2

______ of the equation.
H2O
___ hydrogen atoms + ___ oxygen atoms  ___ oxygen atom and ___ hydrogen atoms
H
H
O
O
H
O
H
 How can you get the number of oxygen atoms on both sides to be the same?
 You ________ change the formula of water to H2O2 because that is the formula for
____________ ____________, a completely different compound.
Step 3: Use Coefficients to Balance Atoms
 To __________ the equation, use coefficients.
 A ____________ is a number placed in front of a chemical formula in an equation, and it
tells you how many ________ or ____________ of a reactant or a product will take
part in the __________.
 If the coefficient is ____, you don’t need to write it.
Now, let’s balance the number of oxygen atoms!
H2
+
O2

H2O
 To balance this equation, we will place the coefficient ___ in front of our product, water.
H2
+
O2
__H2O

H
H
O
H
O
O
H
H
O
H
 Balancing the oxygen atoms throws off the ____________ atoms. There are now ____
hydrogen atoms in the reactants and ________ in the product.
 How can we balance hydrogen?
 Let’s place the coefficient _____ in front of hydrogen on the left side.
___H2
H
H
H
+
O
O2

2H2O
H
H
O
O
H
O
H
H
___ hydrogen atoms + ___ oxygen atoms  ___ oxygen atom and ___ hydrogen atoms
Step 4: Look Back and Check!
 We can make sure the equation is balanced by counting the _______ of each element on
each ________.
2H2
+
O2

2H2O
 This equation tells us that ____ molecules of hydrogen react with ____ molecule of
oxygen to yield _____ molecules of _________.
Practice balancing the following equations:
1. Balance the equation for the reaction of magnesium metal (Mg) and oxygen gas (O2),
forming magnesium oxide (MgO).
2. Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming
sodium oxide (Na2O).
3. Balance the equation for the reaction of tin (Sn) with chlorine gas (Cl2), forming tin
chloride (SnCl2).