1. Classifying Chemical Reactions
Year 10 Chemistry

2. Physical & Chemical Changes
What is the difference between a physical and a chemical change?
A physical change is one in which no new substance is formed, e.g. ice melting.
A chemical change or chemical reaction has occurred if one or more new substances are formed.

3. A permanent colour change
PHYSICAL
CHEMICAL
Changes shape
A permanent colour change
Breaks into smaller pieces
A gas is given off
Dissolves
Change in temperature
Mixed with another substance
Precipitate forms
Changes state
One metal is deposited on another
No new substances formed
New substances are formed

4. Word and formula equations
Word equation hydrogen + oxygen water Formula equation 2H2 + O2 2H2O

5. Symbols used in chemical equations
(s) solid
(l) liquid
(g) gas
(aq) aqueous - the substance is dissolved in water (solution)
 a gas is given off
↓ a precipitate forms (a solid in a solution)

6. 1. Synthesis Reactions
Synthesis reactions occur when two substances (generally elements) combine and form a compound.
Also called combination or addition reactions.
In general: A + B  AB
reactant + reactant  1 product
Example: C + O2  CO2

7. 1. Synthesis Reactions Hydrogen and oxygen yields water
2H2 + O2  2H2O
Magnesium plus nitrogen yields magnesium nitride
3Mg + N2  Mg3N2
Iron and sulfur yields iron(II) sulfide
Fe + S  FeS

8. Practice
Predict the products. Write and balance the following synthesis reaction equations.
Sodium metal reacts with chlorine gas
Na(s) + Cl2(g) 
Solid Magnesium reacts with fluorine gas
Mg(s) + F2(g) 
Aluminum metal reacts with fluorine gas
Al(s) + F2(g) 

9. 2. Decomposition Reactions
Decomposition reactions occur when a compound breaks up into the elements or into a few simpler compounds.
In general: AB  A + B
1 Reactant  Product + Product
Examples:
2H2O  2H2 + O2
2HgO  2Hg + O2

10. Practice
Predict the products. Then write and balance the following decomposition reaction equations:
Solid Lead (IV) oxide decomposes PbO2(s) 
Aluminum nitride decomposes
AlN(s) 

11. Practice
Identify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation:
N2(g) + O2(g) 
BaCO3(s) 
Co(s)+ S(s) 
NH3(g) + H2CO3(aq) 