Predicting Types of Chemical Reactions
COMPOSITION Reactions R + S ----> RS
For example: 2Na + Cl2 ---> 2NaCl
Any time there are just two elements listed as the reactants (left side of arrow) you have a composition reaction.
DECOMPOSITION Reactions RS ----> R + S
For example: 2MgO --->2 Mg + O2
Any time there is just one compound as the reactant you have a decomposition reaction.
There are five different ways that componds can decompose, the way that they do depends on their composition
a.. metallic carbonates, when heated, decompose into metallic oxides and carbon dioxide
Any metal compound that that ends with CO3 is a carbonate.
For example: CaCO3 ---> CaO + CO2
b. metallic hydroxides, when heated, decompose into metallic oxides and water
Any metal compound that that ends with OH is a hydroxide.
For example: Ca(OH)2 ---> CaO + H2O
c. metallic chlorates, when heated, decompose into metallic chlorides and oxygen
Any metal compound that that ends with ClO3 or ClO4 is a chlorate.
For example: Ca(ClO3)2 ---> CaCl2 + 3O2
d. some acids, when heated, decompose into nonmetallic oxides and water
All compounds that begin with Hydrogen are acids. (see exceptions in naming schemata)
For example: H2SO3 ---> SO2 + H2O (These are very rare)
e. some oxides, when heated, decompose
Any compound that ends with the second elemnt being oxygen, is called an oxide.
For example: 2Na2O ---> 4Na + O2
SINGLE-REPLACEMENT Reactions T + RS ----> TS + R
Any time you see a single element reacting with a compound it is a single replacement reaction.
The single element always* changes place with the first element in the compound. *(except for Halogens, see "d")
There are four ways elements replace elements in these reactions.
a. replacement of a metal in a compound by a more active metal
For example: K + NaCl ---> KCl + Na
b. replacement of hydrogen in water by metals
For example: Mg + H2O ---> MgO + H2
c. replacement of hydrogen in acids by metals
For example: Mg + 2HCl ---> MgCl2 + H2
*d. replacement of a halogen by a more active halogen
For example: F2 +2 HCl --->2HF + Cl2
DOUBLE_REPLACEMENT Reactions RS + TU ----> TS + RU
Any time that you have two compounds reacting you have a double replacement reaction.
The first elements trade places with eachother.
For Example: CuSO4 + MgCO3 ---> MgSO4 + CuCO3
COMBUSTION Reactions CxHy + O2 ----> CO2 + H2O
All combustion reactions follow the same format. They will all start with a hydrocarbon (an element composed
of only hydrogen and carbon) and oxygen.
For Example: C6H12 + 9O2 --->6CO2 + 6H2O