To be able to write a balanced equation for a chemical reaction

1
Objectives

1. To be able to write a balanced equation for a
   chemical reaction

2

• A chemical reaction is balanced by using a
  systematic approach

• Write the formulas of the reactants and products
  to give the unbalanced chemical equation.
• Balance by trial and error starting with the most
  complicated molecule(s). Leave pure elements to
  the end.
• At the end check to be sure the equation is
  balanced (same numbers of all types of atoms on
  the reactant and product sides).

3

• Example 

• Hydrogen gas and oxygen gas combine to form
  liquid water.
• Write the formulas of the reactants and products
  to give the unbalanced chemical equation. H2(g)
  O2(g) ? H2O(l)

4
Hydrogen gas and oxygen gas combine to form
liquid water.
5

• Example