Balancing Chemical Equations Chemistry Lesson # 6 Balancing Chemical Equations

Law of Conservation of Mass The Law of Conservation of Mass states that “in a chemical reaction, the total mass of the reactants is always equal to the total mass of the products.” This means that no matter what chemical reaction happens, matter is never created or destroyed. It may change composition, or state, but it does not simply disappear!

Example 1 A solid has a mass of 35 g. When mixed with a solution, the mass of the products is 85 g. What is the mass of the solution?

Example 2 Solution A has a mass of 60 g, and solution B has a mass of 40 g. When they are mixed, a chemical reaction occurs in which a gas is produced. If the mass of the final mixture is 85 g, what mass of gas is produced?

Balancing Just as we can measure the mass of both products and reactants, we can also measure the number of atoms of each element. For example, if there are 2 atoms of carbon required for a reaction to happen, there will be 2 atoms of carbon in the products of that reaction. Sometimes when we write a word equation, there is no balance of atoms between the reactants and products. To ensure a reaction proceeds in the lab, we first need to balance the equation.

Example 1 Al + Fe2O3 → Fe + Al2O3

Example 2 Cu + AgNO3 → Ag + Cu(NO3)2

Example 3 Na + Cl2 → NaCl

Example 4 Nitrogen + Hydrogen → Nitrogen Trihydride

Example 5 Lithium chlorate → lithium chloride + oxygen

Example 6 Tricarbon octahydride + oxygen → carbon dioxide + water