(2.3) Balancing Chemical Equations

(p150)

Conservation of Mass

As we saw in class, the mass of the reactants must equal the mass of the products in a chemical reaction. 

To show that a reaction is balanced, we must write a balanced chemical equation.

In a balanced chemical equation, the number of atoms on each side of the equation is the same.

How To Write a Balanced Chemical Equation

1. The chemical formula for a substance CANNOT be changed!ex. CO2 molecules must stay as CO2

How To Write a Balanced Chemical Equation

2. From the word equation, write the chemical equation using the correct chemical formula for all the substances involved.

ex. The combustion of ethanol (C2H6OH)

ethanol+ oxygen carbon dioxide + water

C2H6OH + O2 CO2 + H2O

How To Write a Balanced Chemical Equation3. Count the number of atoms in both the reactants and

products.4. Multiply each formula by a coefficient to balance the

number of each kind of atom in both the reactants and products.

     

THE RAP SHEET

The RAP sheet is a methodology used to help balance chemical equations.

It helps keep track of the number and kinds of atoms in a chemical equation.

RReactants

AAtoms

PProducts

C

H

O

2

6

3

C2H5OH + O2 CO2 + H2OAdd coefficient 2 CO2

Add coefficient 3 to H2OAdd coefficient 3 to O2

1

2

3

2

5

6

77

TRY THESE Worksheets 2.3 (D) and 2.3

(E)

(2.3) Balancing Chemical Equations

(p150)

ASSIGNMENTS: Workbook p56 p60-63