1. Adapted by T. Trimpe http://sciencespot.net/
Chemical Reactions
and Equations
8th Grade Science
Adapted by T. Trimpe

2. Remember: Chemical Changes
Chemical change: a change that occurs causing the identity of the substance to change
Burning paper
Digesting food
Electrolysis of water
A chemical change is called a chemical reaction

3. Remember: Chemical Reaction
Chemical reaction: occurs when the original substance changes form into a new substance. Some clues to a chemical reaction may include bubbles, smoke, a strong smell, color change, temperature change, or a sizzling sound

4. Chemical Changes Cont’d
Indicators of a chemical change:
Evolution of light
Evolution of heat
Evolution of a gas
Color change
Formation of a precipitate

5. Chemical Equations Depict the kind of reactants and products
and their relative amounts in a reaction.
4 Al(s) O2(g) Al2O3(s)
The letters (s), (g), and (l) are the
physical states of compounds

6. Chemical Equations
Reactants – the substances that exist before a chemical change (or reaction) takes place.
Products – the new substance(s) that are formed during the chemical changes.
CHEMICAL EQUATION indicates the reactants and products of a reaction.
REACTANTS  PRODUCTS

7. Chemical Equations
The number in the front is called a coefficient. It tells you how many molecules in a reaction.
coefficient
4 Al(s) O2(g) Al2O3(s)
subscript
The number to the right of the symbols is called a subscript. It tells you how many of the same atom.

8. Chemical Equations
When a coefficient is in front of a molecule and a subscript for an atom, you will multiply both numbers in order to determine the number of atoms that will be involved in the chemical reaction.
2 Al2O3
Al = 4 O = 6

9. Let’s Practice

10. Let’s Practice Balance Equations

11. Watch the movie and then complete the chart.
Type of Reaction
Definition
 Equation
Synthesis
Decomposition
Single Replacement
Double Replacement
Two or more elements or compounds combine to make a more complex substance
A + B → AB
AB → A + B
Compounds break down
into simpler substances
Occurs when one element replaces another one in a compound
AB + C → AC + B
Occurs when different atoms in two different compounds trade places
AB + CD → AC + BD
A = Red B = Blue C = Green D = Yellow

12. Identifying Chemical Reactions
2. Use colored pencils to circle the common atoms or compounds in each equation to help you determine the type of reaction it illustrates. Use the code below to classify each reaction.
S = Synthesis D = Decomposition SR = Single Replacement DR = Double Replacement
____ P O2 → P4O10 ____ Mg O2 → MgO
____ HgO → Hg O2 ____ Al2O3 → Al O2
____ Cl NaBr → NaCl Br2 ____ H N2 → NH3

13. ____ Na + Br2 → NaBr ____ CuCl2 + H2S → CuS + HCl
____ HgO Cl2 → HgCl O2 ____ C H2 → CH4
____ KClO3  →   KCl  +  O2  ____ S F2 → SF6
____ BaCl2   +   Na2 SO4 →     NaCl   +   BaSO4