1. 4.2 Synthesis and Decomposition Reactions
Chemical Reactions
4.2 Synthesis and Decomposition Reactions

2. Last Class Reviewed chemical reactions and chemical equations
Reviewed how to balance chemical equations

3. Learning Goals We are learning to…
Identify and predict the products of synthesis and decomposition reactions

4. Chemical Reactions
Most chemical reactions can be grouped into 4 categories
Synthesis
Decomposition
Single displacement
Double displacement

5. Synthesis Reactions
Two reactants combine to make a larger/more complex product.
General Formula:
A + B  AB
Example: Synthesis of sodium chloride
Na(s) + Cl(g)  NaCl(s)

6. Example
Write the balanced chemical equation for the reaction of magnesium with oxygen
Identify the reactants
Identify the type of rxn
Predict products
Skeleton equation
Balance

7. Synthesis Reactions (non-metals)
Reactions involving hydrogen
Follow a similar pattern as those involving metals. Although covalent, you can use charges to predict products
Ex: H2(g) + Cl2(g)  2HCl (g)
We can apply the ionic changes of H (+1) and Cl (-1)

8. Example
Write the balanced chemical equation for the reaction of hydrogen with oxygen
Identify the reactants
Identify the type of rxn
Predict products
Skeleton equation
Balance

9. Synthesis Reactions (non-metals)
Reactions not involving hydrogen
Products are difficult to predict
Ex: Depending on reaction conditions
C(s) + O2(g)  CO2(g) or
2C(s) + O2(g)  2CO(g)

10. Synthesis Reactions (non-metals)
Reactions involving compounds
Products may be difficult to predict
Ex: water and carbon dioxide react to form carbonic acid
H2O(l) + CO2(g)  H2CO3(aq)

11. Example
Water reacts with sulfur trioxide in a synthesis reaction to form sulfuric acid
Write the balanced chemical equation, include states.

12. Decomposition Reactions
A reaction in which a larger compound breaks down to form two (or more) simpler products
General Formula:
AB  A + B
Ex: The decomposition of potassium chloride
2KCl(s)  2K(s) + Cl2(g)

13. Decomposition Reactions
Decomposition reactions involving polyatomic ions or molecular compounds can be difficult to predict – do not break apart like binary ionic compounds
Ex: potassium chlorate decomposes to produce potassium chloride and oxygen
KClO3(s)  KCl(s) + O2(g)

14. Example
calcium carbonate decomposes to produce calcium oxide and carbon dioxide
Write the balanced chemical equation, include states.

16. Homework
page 161 # 1-4, 6, 7, 9