1. 5.1 Synthesis and Decomposition Reactions

2. 5.1 Evidence of Chemical Change
Chemical reactions involve chemical changes
Chemical reactions involve the production of new materials (i.e. when wood burns in a campfire, or photosynthesis where water and CO2 are changed to sugar)
It is not always easy to tell if a chemical change has happened

3. 5.1 Evidence of Chemical Change
6 clues a chemical change has happened:
A precipitate is formed; a new product that is an insoluble solid
(2) A gas is formed
(3) A change of color is observed

4. 5.1 Evidence of Chemical Change
6 clues a chemical change has happened:
(4) A new odor might be produced
(5) A change in temperature may occur
(6) Light might be produced

5. 5.1 Classifying Chemical Reactions
The new substances produced during a chemical reaction will depend on the type of the reaction
Understanding the different types of reactions will allow you to identify the products formed
We will study 4 different type of reactions:
Synthesis
Decomposition
Single displacement
Double Displacement

6. 5.1
Synthesis Reactions
Synthesis Reaction: A chemical reaction in which two or more reactants combine to form a new product
General form of a synthesis reaction:
A + B AB +
In a synthesis reaction, two or more reactants (A and B) combine to form one new product (AB)
The reactants may be any combination of elements and compounds – but the products are always compounds

7. + 5.1 Synthesis Reactions: Space Exploration 2H2(l) + O2(l) 2H2O(g)
Synthesis reaction are everywhere; thrust is provided for the space shuttle using a synthesis reaction
Liquid hydrogen and liquid oxygen are mixed which combine to form water vapor
2H2(l) + O2(l) H2O(g) +

8. + 5.1 Synthesis Reactions: Agriculture N2(g) + 3H2(g) 2NH3(g)
Fritz Haber (German chemist) developed a way to make ammonia in 1910
To optimize crop yields, farmers need to supply their crops with fertilizers which are made with ammonia (NH3)
This synthesis reaction is known as the Haber process
N2(g) + 3H2(g) NH3(g) +

9. 5.1 Synthesis Reactions: The Environment
Many atmospheric pollutants are made from synthesis reactions
Nitrogen in the air can combine with oxygen to make nitrogen oxides
Smog is formed in two steps:
(1) N2(g) + O2(g) NO(g) (colorless gas)
(2) 2NO(g) + O2(g) NO2(g) (brown gas)
Read STSE case study page 182 – do questions #1 & 2

10. 5.1 Synthesizing Binary Ionic Compounds
Knowing how elements combine, it is possible to predict the products of simple synthesis reactions
Example: Complete and Balance the following synthesis reaction:
Na(s) + Cl2(g)

11. 5.1 Synthesizing Binary Ionic Compounds
Example: Complete and Balance the following synthesis reaction:
Na(s) + Cl2(g)
Solution:
Charges: Na1+ and Cl1- (they combine 1:1 ratio)
Skeleton equation: Na(s) + Cl2(g) NaCl(s)
Balanced equation: 2Na(s) + Cl2(g) NaCl(s)
Do practice questions # 1-2 on page 184
Do Learning Check questions # 1-4 on page 185

12. + 5.1 Decomposition Reactions
Decomposition Reaction: A chemical reaction in which a compound breaks down into two or more products
General form of a decomposition reaction:
AB A + B +
The products may be any combination of elements and compounds – but the reactants are compounds

13. + 5.1 Decomposition Reactions: Hydrogen fuel cells
It is important to have enough hydrogen gas for the development of new fuel cell technologies
One way to make hydrogen gas is electrolysis; a decomposition reaction that breaks down water
2H2O(l) H2(g) + O2(g) +

14. 5.1 Decomposition Reactions: Explosives
Explosives often involve decomposition reactions
TNT or trinitrotoluene decomposes into 3 gases nitrogen, water and carbon monoxide with explosive force
2C7H5N3O6(s) N2(g) + 5H2O(g) + 7CO(g) C(s)

15. Elements formed from Decomposition of Ionic Compounds
5.1
Elements formed from Decomposition of Ionic Compounds
Complete and balance the following decomposition reaction:
AgCl(s)

16. Elements formed from Decomposition of Ionic Compounds
Solution:
This decomposition reaction produces silver and chlorine
Silver is a metal Ag(s) and Chlorine is a diatomic gas Cl2(g)
Skeleton equation AgCl(s) Ag(s) + Cl2(g)
Balanced equation AgCl(s) Ag(s) + Cl2(g)
Do practice questions # 1-3 on page 187
Do review questions # 1-8 on page 189