Balancing Equations

Science, Grade 6


Table Of Contents: Balancing Equations

1. Conservation of Mass
In any chemical reaction, atoms are never lost or gained, they are only rearranged. All atoms of the reactants are converted to atoms of the products, which is the reason chemical equations are balanced. The Law of Conservation of Mass states that the mass of the reactants must equal the mass of the products. To find the mass of a molecule, add the atomic masses of each element. For example, in the equation, C + O₂ -> CO₂, the mass of the reactants is 12 + 2 x 16 which equals 44 amu. The mass of CO₂ is also 44 amu. Therefore, the mass of the reactants equals the mass of the products so the equation is balanced.
2. Balancing Chemical Equations
To balance a chemical equation, you apply the Law of Conservation of Mass to get the same number of atoms of every element on each side of the equation. The first step in balancing an equation is to make a list of how many atoms of each element are on each side of the equation. The coefficients are in front of the molecules that tell you how many of each molecule there are. Balance the atoms one at a time by changing the coefficients in front of each formula until you have an equal number of each type of atom on both sides of the equation. Never change the subscripts. The coefficient times the subscript gives the total number of atoms. It is usually easier to first balance the atoms that occur in one substance on each side of the equation. Then balance the atoms that occur in compounds, before attempting to balance atoms that occur in elemental form such as H₂, O₂or Cl₂. And finally, be sure that all the coefficients are in the smallest possible whole number ratio.
3. Example of Balancing a Chemical Equation
Let’s balance the equation, N₂+H₂ -> NH₃. There are two atoms of nitrogen and hydrogen on the left side and one nitrogen atom and three hydrogen atoms on the right side. First balance the atoms in the compound, NH₃. Place a 2 in front of NH₃ which now makes it 2 atoms of N and 6 atoms of H on the right side of the equation. This balances the N atoms on each side of the equation but not the H. By placing a 3 in front of the H atom on the left side, it increases the H atoms on the left side of the equation to 6, which makes it equal to the number of H atoms on the right side. The equation is now balanced. It tells us that 1 molecule of nitrogen combines with 3 molecules of hydrogen to produce 2 molecules of ammonia.