1. Introduction to Chemistry
2. The Periodic Table
3. Quantum Numbers
4. Electron Configuration
5. Chemical Families
6. Oxidation Numbers
7. Chemical Formulas
8. Chemical Names
9. Formula Mass
10. Percentage Composition
11. Reaction Types
12. Balancing Equations
13. The Mole Concept
14. Solution Concentration
16. Kinetic Theory
17. The Gas Laws
18. Enthalpy & Heat
19. Reaction Rates
20. Acids & Bases
21. pH Scale
23. Net Ionic Equations
24. Redox Reactions
25. Organic Chemistry
26. Nuclear Chemistry
12. Balancing Chemical Equations
Atoms are neither created nor destroyed during any chemical reaction. Chemical changes merely rearrange the atoms.
The statement above is supported by:
Chemical reactions are represented in a concise way by chemical equations.
2 H2 + O2 → 2 H2O
A chemical equation must have the same number of atoms of each element on both sides of the arrow. When this condition is met, the equation is said to be balanced.
- The reacting substances, called reactants, are located on the left side of the arrow.
- The substances formed, called products, are located on the right side of the arrow.
- In a chemical equation, the + sign is read as "reacts with" and the arrow is read as "produces".
- Numbers in front of the formulas are coefficients, indicating the relative number of molecules or ions of each kind involved in the reaction.
Coefficients of 1 are never written - they are understood.
- Numbers to the lower right of chemical symbols in a formula are subscripts, indicating the specific number of atoms of the element found in the substance.
Subscripts of 1 are never written - they are understood.
To count atoms, multiply the formula's coefficient by each symbol's subscript.
For example: 2Al2(SO4)3
- For Al - coefficient of 2, times subscript of 2 = 4 aluminum atoms
- For S - coefficient of 2, times subscript inside parenthesis of 1, times subscript outside parenthesis of 3 = 6 sulfur atoms
- For O - coefficient of 2, times subscript inside parenthesis of 4, times subscript outside parenthesis of 3 = 24 oxygen atoms
The order in which the following steps are performed is important. While shortcuts are possible, (and you will learn about one), following these steps in order is the best way to be sure you are correct.
Balance equations "by inspection" with these steps:
HINT: NEVER change subscripts to balance equations.
- Check for diatomic molecules.
- Balance the metals (not Hydrogen).
- Balance the nonmetals (not Oxygen).
- Balance oxygen.
- Balance hydrogen.
- The equation should now be balanced, but recount all atoms to be sure.
- Reduce coefficients (if needed). ALL coefficients must be reducable before you can reduce. An equation is not properly balanced if the coefficients are not written in their lowest whole-number ratio.
The physical state of each substance in a reaction may be shown in an equation by placing the following symbols to the right of the formula:
- (g) for gas
- (l) for liquid
- (s) for solid
- (aq) for aqueous (water) solution
86 Equations to practice balancing
Balancing Equations #1
Balancing Equations #2