1. 4.2 Synthesis and Decomposition Reactions

2. Synthesis Reactions
Involves smaller atoms or molecules combining to form a larger molecule
Two or more reactants combine to make one product
element + element → compound
Synthesis reactions of non-metals create molecular compounds
Synthesis reactions can involve compounds coming together
compound + compound → new compound

4. General Equation

5. Synthesis Reactions involving Hydrogen
Usually forms a molecular compound
H2(g) + Cl2 (g) → HCl(g)
H2(g) + Cl2 (g) → 2HCl(g)

6. Example Ex. 1) Hydrogen + oxygen → water H2(g) + O2(g) → H2O (l)
2H2(g) + O2(g) → 2H2O (l) balanced!

7. Synthesis Reactions Involving Other Reactions
Can be more difficult to predict
C(s) + O2 (g) → CO2(g) OR
2 C(s) + O2(g) → 2 CO(g)
In these cases, the only way to identify the reaction products is by conducting chemical tests.

8. Examples Sodium + chlorine → sodium chloride
Na (s) + Cl2(g) → NaCl (s)
2Na(s) + Cl2(g) → 2NaCl(s)
3 )Copper + Oxygen → copper (ll) oxide
Cu(s) + O2(g) → CuO(s)
2Cu(s) + O2(g) → 2CuO(s)

9. Synthesis Involving Compounds
This is an important reaction that impacts aquatic ecosystems.
Carbonic Acid: raises the pH of our oceans. Eats at the shells of shelled animals and causes other problems for ocean life.
CO2 (aq) + H2O → H2CO3 (aq)

10. Decomposition Reaction
Opposite to synthesis
Involves a large molecule splitting to form smaller molecules or elements
One reactant breaks apart into two or more products
The general equation for a decomposition reaction is:
compound → element + element

11. Examples! 1) Water → Hydrogen + Oxygen H2O (l) → H2 (g) + O2 (g)
2) Triiodine mononitride→ Nitrogen + Iodine
l3N (s) → N2(g) + l2 (l)
2l3N (s) → N2(g) + 3l2 (l) balanced!