Completing Chemical Reactions

Completing Chemical Reactions
 If you only know the reactant(s) in a reaction, you can predict what products will form!
 Each type of reaction has a specific pattern. Use this to help you!
Steps to follow
1. Identify Reactant(s)
2. Identify Reaction Type
3. Predict the products using the rules for the specific reaction type
◦ If the new products are ionic, you MUST do a new “criss cross” to determine the
formula of the new compound(s)
4. Balance the Equation
1. Synthesis Reactions
(a) Metal + non-metal  Ionic compound
◦ Combine the two elements into a compound
◦ Use criss-cross rule to determine formula of new compound!
Ex:
Li
+
Cl2

Ex:
Al
+
O2

(b) non-metal + non-metal  molecular compound
◦ Simply combine the two elements into a compound, leaving the subscripts the same.
Ex:
S
+
Br2

Ex:
C
+
O2

2. Decomposition Reactions
A. Binary compounds
o Compound  element + element
o Break down into their two elements (HOFBrINCl still applies!)
Ex: H2O 
Ex: MgCl2 
B. Carbonates
o When a compound with carbonate (CO3) in it decomposes, Carbon dioxide is ALWAYS
formed
o The other compound is a metal oxide (compound containing the metal and oxygen)
Ex: MgCO3 
Ex: Na2CO3 
3. Single Displacement Reactions
o The two metals switch places OR the two non-metals switch places
o MUST do a new criss-cross on the new compound!! DO NOT just carry over the
subscripts
o If a multivalent metal exists, determine its charge from the reactant formula
Ex: Mg
+
CuCl2
Ex: KBr
+
l2


4. Double Displacement Reactions
A. Precipitation Reactions
o Two aqueous compounds combine and form a solid product (precipitate) in a solution
o Switch the cations between the two compounds
o Do new criss-crosses to determine new formulas!

Ex:
NaCl
+
BeO
Ex:
KI
+
Pb(NO3)2

5. Combustion Reactions
A. Complete combustion of a hydrocarbon
o Two products are always CO2 and H2O
Ex: Complete combustion of C6H14 (hexane – used in shoe glue)
Practice:
+
O2
→
1.
Ag
2.
Na2S
+
Cl2
→
3.
CaO
+
KCl
→
4.
HgO
→
5.
CaCO3
6.
Al
7.
C2H6 +
+
→
FeO
→
O2
→