CHAPTER 6
NOTHING IS LOST, NOTHING IS GAINED
BALANCING EQUATIONS
A chemical reaction begins with two molecules that react together to form new
molecules.
Let’s look at a reaction:
K
+
H 2O
->
KOH +
H2
What molecules are the reactants?
What molecules are the products?
This equation is not balanced. This means that the number of atoms of each element
before the arrow is not the same as that after the arrow.
How many Potassium atoms are there before the arrow?
How many Potassium atoms are there after the arrow?
How many Oxygen atoms are there before the arrow?
How many Oxygen atoms are there after the arrow?
How many Hydrogen atoms are there before the arrow?
How many Hydrogen atoms are there after the arrow?
So how can we balance this equation?
We need to add coefficients in front of each molecule in the reaction. The coefficient is
a multiplication factor.
For example, if we write 2 H2O, this means there are two water molecules.
How many Hydrogen atoms are there in 2 H2O?
How many Oxygen atoms are there in 2 H2O?
Write the coefficient of each molecule in the boxes of the reaction below.
Hint: Start with Potassium, Oxygen then Hydrogen. Use a pencil because you may to
erase…
Balance the following equations:
N2
+
O2
->
NO2
Fe
+
H 20
->
Fe3O4
+
H2
Hint: start with Fe, O then H
Al
+
HCl
->
AlCl3
+
H2
Hint: start with Al or Cl, then O, then H
Homework Questions 6.1 - 6.4
Hint: start with N then O
NEUTRALIZATION EQUATIONS
Balance the following neutralization equations:
HCl
+
NaOH
H2SO4
+
->
NaOH
NaCl +
->
H 2O
Na2SO4
Hint: Start with Na or Cl, then O , then H
+
H 2O
Hint: start with Na or SO4 (as a whole group), then O, then H
Why are the above equations considered neutralization reactions?
Complete the following neutralisation equations:
HBr
+
Ba(OH)2 --->
HNO3
+
Ca(OH)2 --->
Homework Questions 6.15-6.16
STOICHIOMETRIC CALCULATIONS
Let’s look at the following balanced equation: 2 SO2
+
O2
->
2 SO3
How many moles of SO2 are needed to react with 1 mole of O2 to produce 2
moles of SO3?
If we had 2 moles of O2, how many moles of SO2 would be needed to make
SO3?
If I had 96 g of O2 , how many grams of SO2 would be needed to make SO3?
Show your work here:
Homework Questions 6.5- 6.14