1. Balancing Chemical Equations Science 10 Chemical Reactions

2. What is a Chemical Equation? A chemical equation is simply a way to represent a chemical reaction on paper. A typical chemical equation looks like this: 2H 2 + O 2  2H 2 O

3. Why Balance Equations? Chemical equations must be balanced because atoms can be neither created nor destroyed in an ordinary chemical reaction. Therefore, there must be the same number of each type of atom on each side of the chemical equation.

4. Numbers in Chemical Equations There are two types of numbers found in chemical equations: Subscripts – the small numbers to the lower right of chemical symbols. They represent the number of atoms of each element in the molecule. Coefficients – the large numbers in front of chemical formulas. Coefficients represent the number of molecules of the substance in the reaction.

5. Numbers (cont’d) You can change any coefficient in a chemical equation. You can not change the subscripts in a chemical equation. To do so would change the compound.

6. Determining the Number of Atoms To determine the number of any particular type of atom in a chemical equation simply multiply the coefficient in front of the compound by the subscript following the chemical symbol for the atom.

7. Example 2NaOH  Na 2 O + H 2 O On the left hand side of the equation there are: 2 sodium (Na) atoms – (2 × 1) 2 oxygen (O) atoms – (2 × 1) 2 hydrogen (H) atoms – (2 × 1) On the right hand side of the equation there are: 2 sodium atoms (1 × 2) 2 oxygen atoms ((1 × 1) + (1 × 1)) 2 hydrogen atoms (1 × 2)

8. Balancing Equations by Inspection 1. Check for diatomic molecules (H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 ) If these elements appear by themselves (not in a compound) they must be written with the subscript 2. 2. If any polyatomic ions exist on both sides of the reaction, balance them. 3. Balance any metal atoms.

9. Balancing (cont’d) 4. Balance any non-metal atoms (except hydrogen and oxygen). 5. Balance oxygen atoms. 6. Balance hydrogen atoms. 7. Check your work by recounting all atoms.

10. Balancing (cont’d) 8. If every coefficient will reduce, rewrite the equation in the simplest whole-number ratio. An equation is not properly balanced if the coefficients are not written in their lowest whole-number ratio.