1. Balancing Chemical Equations

2. What is a chemical equation?
Chemical equation - Describes a chemical change.
Parts of an equation:
Reactant
Product
2Ag + H2S
Ag2S + H2
Reaction symbol

3. Reactants and Products
Reactant - The chemical(s) you start with before the reaction.
Written on left side of equation.
Product - The new chemical(s) formed by the reaction.
Right side of equation.

4. Subscripts and Coefficients
Subscript - shows how many atoms of an element are in a molecule.
EX: H2O
2 atoms of hydrogen (H)‏
1 atom of oxygen (O)‏
Coefficient - shows how many molecules there are of a particular chemical.
EX: 3 H2O
Means there are 3 water molecules.

5. A Chemical Reaction
2H2 + O2  2H2O

6. Law of Conservation of Mass
In a chem. rxn, matter is neither created nor destroyed.
In other words, the number and type of atoms going INTO a rxn must be the same as the number and type of atoms coming OUT.
If an equation obeys the Law of Conservation, it is balanced.

7. An Unbalanced Equation
CH4 + O2  CO2 + H2O
Reactant Side
Product Side
1 carbon atom
4 hydrogen atoms
2 oxygen atoms
1 carbon atom
2 hydrogen atoms
3 oxygen atoms

8. A Balanced Equation CH4 + 2O2  CO2 + 2H2O Reactant Side Product Side
1 carbon atom
4 hydrogen atoms
4 oxygen atoms
1 carbon atom
4 hydrogen atoms
4 oxygen atoms

9. Rules of the Game 1. Matter cannot be created or destroyed.
2. Subscripts cannot be added, removed, or changed.
3. You can only change coefficients.
4. Coefficients can only go in front of chem. formulas...NEVER in the middle of a formula.
A few extra tips:
Try balancing big formulas first; save free elements for last.
If the same polyatomic ion appears on both sides of the equation, it’s usually okay to treat it as one unit.
There is no one particular way to balance equations. Some equations are harder to balance than others and might require some creativity to solve.

10. Balancing Equations 3 2 2 2 1 6 2 6 3 N2 + H2  NH3 N H
Balance the following equation by adjusting coefficients.
N H2  NH3 3 2
reactants
products N 2 2 1 6 2 6 3 H

11. Balancing Equations 3 2 2 2 1 1 2 2 1 2 1 6 3 2 6 KClO3  KCl + O2 K
Balance the following equation by adjusting coefficients. 3 2
KClO3  KCl + O2 2
reactants
products K 2 1 1 2 Cl 2 1 2 1 6 3 2 6 O

12. Balancing Equations 4 6 7 2 Balance the following equation:
C2H6 + O2  CO2 + H2O 4 6 7 2

13. Balancing Equations 2 3 4 Balance the following equation:
Fe + O2  Fe2O3 2 3 4

14. Homework ____ K + ____ Cl2  ____ KCl
____ N2 + ____ H2  ____ NH3
____ NaF + ____ Br2 ____ NaBr + ____ F2
____ Pb(OH)2 + ____ HCl  ____ H2O + ____ PbCl2
____ AlBr3 + ____ K2SO4  ____ KBr + ____ Al2(SO4)3
____ CH4 + ____ O2  ____ CO2 + ____ H2O
____ Na3PO4 + ____ CaCl2  ____ NaCl + ____ Ca3(PO4)2
____ K + ____ Cl2  ____ KCl
____ Al + ____ HCl ____ H2 + ____ AlCl3