Representing chemical change
Chemical change is represented by an equation that has the form reactants 
products.
The first step in writing a chemical equation using symbols is to write formulae for all of the reactants and products as shown for the reaction of hydrogen and oxygen below.
Then count the atoms as is shown in the table.
Then balance the equation by adjusting the numbers in front of the formulae These numbers are referred to as coefficients.
products.The first step in writing a chemical equation using symbols is to write formulae for all of the reactants and products as shown for the reaction of hydrogen and oxygen below.
| H2 | + | O2 | | H2O | |
| atom count | 2 H | 2 O | 2 H 1 O |
Formulae for reactants and products are included in all of the equations in this module.
Then count the atoms as is shown in the table.
This equation is not consistent with the experimental fact that the total mass of the reactants of a chemical reaction always equals the total mass of the products. Chemists say that the equation is not balanced.
Balanced equations have the same number and type of atoms in the reactant substances as in the product substances.
Then balance the equation by adjusting the numbers in front of the formulae These numbers are referred to as coefficients.
| Balanced: | 2H2 | + | O2 | | 2H2O |
| atom count | 4 H | 2 O | 4 H 2 O |
Do not change the subscripts in the formulae for the particles.
The numbers of a particular particle involved depends on the nature of the chemical change, but the composition of the particle is constant!
The numbers of a particular particle involved depends on the nature of the chemical change, but the composition of the particle is constant!