Chemical Reactions
4.2
Synthesis and Decomposition Reactions
Last Class
• Reviewed chemical reactions and chemical
equations
• Reviewed how to balance chemical equations
Learning Goals
• We are learning to…
– Identify and predict the products of synthesis
and decomposition reactions
Chemical Reactions
• Most chemical reactions can be grouped into
4 categories
1.
2.
3.
4.
Synthesis
Decomposition
Single displacement
Double displacement
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)
Example
Write the balanced chemical equation for the
reaction of magnesium with oxygen
1.
2.
3.
4.
5.
Identify the reactants
Identify the type of rxn
Predict products
Skeleton equation
Balance
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)
Example
Write the balanced chemical equation for the
reaction of hydrogen with oxygen
1.
2.
3.
4.
5.
Identify the reactants
Identify the type of rxn
Predict products
Skeleton equation
Balance
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)
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)
Example
Water reacts with sulfur trioxide in a synthesis
reaction to form sulfuric acid
– Write the balanced chemical equation, include
states.
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)
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)
Example
• calcium carbonate decomposes to produce
calcium oxide and carbon dioxide
• Write the balanced chemical equation, include
states.
Homework
page 161
# 1-4, 6, 7, 9