1. 3.2 Synthesis, Decomposition and Combustion Reactions

2. Chemical Reactions Synthesis/Combination Decomposition Combustion
Chemical reactions can be grouped into five categories:
Synthesis/Combination
Decomposition
Combustion
Single displacement
Double displacement

3. Synthesis and Decomposition Reactions
Chemistry
Prom
2014!
Synthesis and Decomposition Reactions

4. Let’s come together….
Synthesis reaction – two more substances combine to form one new substance
Two substances dancing alone decide to hook up… become a happy couple A + B  AB
Geez I could use a mate.
Man I’m lonely
Satisfaction 

5. Synthesis Reaction Let’s come together….
Usually exothermic (energy is produced)
Can occur naturally or by an initial application of energy (heat, flame, UV light, use of catalyst)
Let’s come together….

6. Synthesis Reaction Let’s come together…. Geez I could use a mate.
Man I’m lonely
Satisfaction 
Let’s come together….

7. Practice DIATOMIC ALERT! Al (s) + O2 (g)  Al3+O2- Al2O3 AlO
Show the synthesis of solid aluminum and oxygen gas.
What are the reactants?
Al + O2
What are the products?
It’s a synthesis reaction, so we know Al and O are going to make a compound….
If the products aren’t in the question you need to KRISS KROSS to figure it out!
DIATOMIC ALERT!
Al (s) + O2 (g) 
Al3+O2-
Al2O3
AlO

8. Practice A, B, and D C + O2  CO2 CaO + H2O  Ca(OH)2 H2O  H2 + O2
Which reactions are SYNTHESIS reactions?
C + O2  CO2
CaO + H2O  Ca(OH)2
H2O  H2 + O2
2Na + Cl2  2NaCl
Fe + CuSO4  FeSO4 + Cu
2K3PO4 + 3H2SO4  3K2SO4 + 2H3PO4
A, B, and D

9. Predicting Products
Metal + oxygen → metal oxide (basic oxide)
EX. 2Mg(s) + O2(g) → 2MgO(s)
Nonmetal + oxygen → nonmetallic oxide (acidic oxide)
EX. C(s) + O2(g) → CO2(g)
Metal oxide + water → metallic hydroxide (base)
EX. MgO(s) + H2O(l) → Mg(OH)2(s)
Nonmetallic oxide + water → acid
EX. CO2(g) + H2O(l) → ; H2CO3(aq)
Metal + nonmetal → salt
EX. 2 Na(s) + Cl2(g) → 2NaCl(s)
A few nonmetals combine with each other.
EX. 2P(s) + 3Cl2(g) → 2PCl3(g)
These two reactions must be remembered:
N2(g) + 3H2(g) → 2NH3(g)
NH3(g) + H2O(l) → NH4OH(aq)

10. I don’t think this is working out…
Decomposition reaction – one substance breaks into multiple substances
A couple decides…well it is time to break up AB  A + B
Satisfaction!
I want to see other people
I don’t think this is right for us…
Satisfaction!

11. Decomposition Reaction
Usually endothermic (requires energy)
Can require energy in the form of heat, electricity, catalyst, UV light
*some decomposition rxns occur at room temperature

12. Decomposition Reaction
AB  A + B
Eg. 2H20  2H2 + O2
2NaCl (s)  2Na (s) + Cl2(g) (heat/electricity required)

13. Decomposition Reaction
I don’t think this is right for us…
Satisfaction!
I want to see other people
Satisfaction!

14. Don’t forget to balance!
Practice
Show the decomposition water after electricity has passed through it.
What are the reactants?
Water! H2O
What are the products?
It’s a decomposition reaction, so we know the elements in water are going to break apart
The question will specify if any compounds are formed
DIATOMIC ALERT!
H2O 
H2 + O2
H + O
Don’t forget to balance!

15. More Practice! C, D and F C + O2  CO2 CaO + H2O  Ca(OH)2
Which reactions are DECOMPOSITION reactions?
C + O2  CO2
CaO + H2O  Ca(OH)2
H2O  H2 + O2
H2SO4 H2 + S + 2O2
Fe + CuSO4  FeSO4 + Cu
K3PO4  K3P + 2O2
C, D and F

16. Predicting Products
Metallic carbonates, when heated, form metallic oxides and CO2(g).
EX. CaCO3(s) → CaO(s) + CO2(g)
Most metallic hydroxides, when heated, decompose into metallic oxides and water.
EX. Ca(OH)2(s) → CaO(s) + H2O(g)
Metallic chlorates, when heated, decompose into metallic chlorides and oxygen.
EX. 2KClO3(s) → 2KCl(s) + 3O2(g)
Some acids, when heated, decompose into nonmetallic oxides and water.
EX. H2SO4 → H2O(l) + SO3(g)
Some oxides, when heated, decompose.
EX. 2HgO(s) → 2Hg(l) + O2(g)
Some decomposition reactions are produced by electricity.
EX. 2H2O(l) → 2H2(g) + O2(g)
EX. 2NaCl(l) → 2Na(s) + Cl2(g)

17. Combustion Reactions
When a compound or element is reacted with O2 (g) to form the most common oxides that make up that compound.
-These reactions usually accompany heat and light.
Complete combustion – products H2O and CO2
Incomplete Combustion - products H2O and CO

18. Combustion Reactions
Combustion reactions occur when a hydrocarbon reacts with oxygen gas.
This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: 1) A Fuel (hydrocarbon) 2) Oxygen to burn it with 3) Something to ignite the reaction (spark)

19. Combustion Reactions In general: CxHy + O2  CO2 + H2O
Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide)
Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)

20. Combustion Reactions
Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.