Synthesis (or Combination) Reactions
Now that we know the parts of chemical equations and how to balance them we can talk about the four main
classes that most chemical reactions fall under.
The first type of reactions that we’ll talk about are called Synthesis, or Combination reactions. These reactions
are when two or more substances combine to form a new compound, usually 2 elements bonding, or possibly a
compound combining with an element.
General Formula:
A + B  AB
An example of this is when I burned a piece of magnesium metal and it became magnesium oxide. You could
tell that it was a chemical reaction because the shiny metal turned in to a white powder.
2Mg + O2 
A
2MgO
B
AB
We started with a solid, silver metal and a colorless gas and ended up with a white powder. Another example of
a combination reaction is the synthesis of table salt from sodium and chlorine. I have a short video clip to show
you that.
Synthesis reactions don’t always have to be just the combination of 2 elements; they can be the combination of
two compounds also. A combination reaction happens all the time in bottles of soda. Have you ever heard that
you can remove rust with Coke? You can because a weak acid is formed as the bottle sits. What are the two main
components of Coke (besides sugar)?Carbon dioxide and water
CO2 + H2O  H2CO3
Carbon dioxide plus water yields carbonic acid
Let’s practice balancing and writing the names in the following synthesis reactions:
Cu(s)
+
 CuO(s)
O2(g)
____________ + ____________  ___________________
Ba(s)
+
 BaS(s)
S8(s)
____________ + ____________  ___________________
Write the symbols for each formula, then balance the equation
(Watch out for diatomics! Remember HOFBrINCl)
a.
b.
Potassium
+
Bromine

Potassium Bromide
____________ + ____________
 ___________________
Cobalt

+
Fluorine
____________ + ____________
Cobalt (II)Fluoride
 ___________________
See if you can predict the products in the following reactions then complete and balance them
a. Sodium + Fluorine 
b. Aluminum + Chlorine 
The second type of reaction is sort of the opposite of a combination reaction – a decomposition, or analysis
reaction
Decomposition Reactions (Analysis Reactions)
General Formula:
Notes:
AB

A
+
B
- a single compound undergoes a reaction that produces 2 or more simpler substances
- Usually a compound breaks down into 2 elements
An example of this is the reaction that happens when an airbag in a car inflates.
2NaN3(s)

2Na(s) +
3N2(g)
AB
A
B
Balance each of the following equations by inserting the proper coefficients where needed. Write the name of
the reactants and products underneath each formula.
a.
HgO

Hg
+
O2(g)
_________________  ______________ + _________________
b.
N2O(g)

N2(g)
+
O2(g)
_________________  ______________ + _________________
Write the name of each formula, then balance the equation (Watch out for diatomics!)
a.
Silver Oxide 
Silver
+
Oxygen
_________________  ______________ + _________________
b. Calcium Carbonate
_____________
Calcium Oxide
 ______________
c. Hydrogen nitrate 
Water +
____________  ___________

Carbon Dioxide
+ ______________
Nitrogen
+
Oxygen
+ __________ + __________
Complete and balance the following reactions
c. Barium Chloride 
d. Magnesium Bromide
+