1. Balancing Chemical Equations
Created by: Mrs. Dube

2. Law of Conservation of Mass
Law of Conservation of Mass states that in a chemical reaction atoms are neither created nor destroyed.
Whatever reactants you start with, you will have the same number of atoms in the products
All atoms present in the reactants are also present in the products

3. Chemical Equations
Chemical equations represent how atoms are rearranged in a chemical reaction
The atoms in the reactants are shown on the left side of the equation
The atoms in the products are shown on the right side of the equation

4. In order to write a chemical equation, you
must know the following information:
the reactants and products
the atomic symbols and chemical formulas
of the reactants and products
the direction of the chemical reaction
The arrow shows the direction in which the
reaction proceeds

5. Balancing Equations
Chemical equations must follow the Law of Conservation of Mass
The same number of atoms must appear on both sides of the equation
You have to balance the equation to make the number of atoms equal on each side of the equation

6. Balancing Equations
To balance a chemical equation, the first thing you have to do is count the number of atoms of each element shown in the equation
Now check to see how many atoms of that element are shown on the product side of the equation

7. Balancing Equations
You can balance chemical equations by changing a reactant’s or product’s coefficient
A coefficient indicates how many molecules take part in the reaction (ex. 2H2O shows 2 water molecules)
If there is no coefficient, then there is only one molecule of that type in the reaction

8. Using Coefficients To Balance Equations
Only coefficients can be changed to balance chemical equations!
Subscripts are part of the chemical formula for the reactants and products and cannot be changed to balance an equation
Changing a subscript changes the substance represented by the formula

9. Using Coefficients To Balance Equations
Balancing the equation: N2 + H2  NH 3
First, count the atoms of the reactants:
N= 2 atoms; H=2
Next, count the atoms of the products:
N=1; H=3
Use a coefficient to add atoms to one side of the equation (try 2 to start out)
DO NOT CHANGE THE SUBSCRIPTS

10. Using Coefficients To Balance Equations
Look at the second atom of the reactants and the second atom of the product and compare the number of atoms
Add a coefficient to the second reactant to balance the number of atoms
Now, count up all the atoms to make sure that the equation is balanced

11. Using Conservation Of Mass
Balance the following equations:
Hg + O2  HgO
N2 + O2  NO2
Zn + HCl  ZnCl2 + H2
N H2  NH3
Why are coefficients changed but subscripts are not changed when balancing chemical equations?