Balancing Chemical Equations

Chapter 7

What is Balancing?

• Making sure there are equal numbers of each type of atom on each side of a chemical reaction

• Reactants = products

• Why do this???????

Law of Conservation of Mass

• Matter is neither created or destroyed in a chemical reaction.

What does this mean?

Atoms are not created or destroyed during a chemical reaction.

-The number and types of atoms do not change -- atoms are just rearranged mass of the = mass of the reactants products

There must be the same number of each element on both sides of the equation.

reactants

products

• When balanced.

# of reactant atoms = # product atoms

• If you put 3 oxygen in on the left side, then you must get out 3 oxygen on the right side.

To BALANCE:1. Only change Coefficients

2. Do not change the subscripts.

(Only change the numbers in front of each compound or

atom.)

Steps for Balancing Equations

1. Write the formulas for the reactants and products, put in equation form (skeleton equation with no coefficients) – might be done for you.

2. Count the number of atoms of each element on both sides of the yield arrow.

3. Balance atoms by adding coefficients (prefixes) to appropriate formulas

4. Check work by recounting atoms of each elements.

Example1: Ca + O2 → CaO

(calcium) (Oxygen gas) (Calcium Oxide)

Reactants ProductsCalcium 1 1Oxygen 2 1

- Calcium is balanced, oxygen is not

- Use coefficients to balance the number of oxygen atoms

- Now the calciums are unbalanced so need another coefficient

22

2

2 2

Example2: H2 + O2 → H2O

Reactants Products

Hydrogen 2 2Oxygen 2 1

- Hydrogen is balanced, oxygen is not

- Use coefficients to balance the number of oxygen atoms

- Now the hydrogens are unbalanced so so need another coefficient.

22

2

4 4

Example2:NaCl → Na + Cl2

Reactants Products

Sodium 1 1Chlorine 1 2

- Sodium is balanced, chlorice is not- Use coefficients to balance the

number of chlorine atoms- Now the sodium are unbalanced

so so need another coefficeint.

2 2

22

2

Example 3: Fe + O2 → Fe2O3

Reactants ProductsIron 1 2Oxygen 2 3

Both the iron and oxygen are unbalanced.Tip: Sometimes it helps to balance the oxygen

atoms first.The least common multiple between 2

and 3 is 6Now the Iron has to be balanced

23

66

4

4

4

The End