Decompostion Reaction

Important notes to remember: (1) NONE of the equations are balanced!! and (2) make sure to write correct formulas. DO NOT just copy the subscripts from the reactants over into the products.

During decomposition, one compound splits apart into two (or more pieces). These pieces can be elements or simpler compounds

Written using generic symbols, it is usually shown as:

AB ---> A + B

However, that really only works for splitting apart into the elements, like these examples.

HgO ---> Hg + O2 H2O ---> H2 + O2 MgCl2 ---> Mg + Cl2 FeS ---> Fe + S

Decomposition can also split one compound into two simpler compounds (or compound and an element) as in these examples:

CaCO3 ---> CaO + CO2 Na2CO3 ---> Na2O + CO2 KClO3 ---> KCl + O2 Ba(ClO3)2 ---> BaCl2 + O2

Notice how, in every case so far, there is only one substance on the left-hand (reactant) side. This is always the case in a decomposition reaction. Don't forget that!!

Figuring out what the products are in decomposition is harder (maybe you'll think it's easier!!) because you will have to recognize several categories of decomposition reactions. Here are your first (yes, there's more!) three:

1) All binary compounds (like the four in the first example set above) will break down into their elements. 2) All carbonates (like the first two in the second example set above) break down to the oxide and carbon dioxide. 3. Chlorates (like KClO3 and Ba(ClO3)2 in the example) will break down to the binary salt and oxygen.

Here is one more category of decomposition reactions:

Ca(OH)2 ---> CaO + H2O NaOH ---> Na2O + H2O HNO3 ---> N2O5 + H2O H3PO4 ---> P2O5 + H2O

The first two substances are bases and the last two are acids. In each case, the acid or base breaks down into the oxide of the metal (in the case of bases) or the oxide of the nonmetal (in the case of acids) plus water.

Here is one example of each category which are then solved below:

1) NaClO3 ---> 2) Li2CO3 ---> 3) KOH --->

https://www.youtube.com/watch?v=8Md_QVh87EI

4) NaCl --->

Example #1

How to figure out the right (or product side):

(1) Identify the type of compound decomposing:

NaClO3 is a chlorate

Notice that you have to be able to "read" a formula and identifiy the parts (cation and anion) that make it up.

(2) Apply the rule for that type:

chlorates decompose to the binary salt and oxygen gas

(3) Write two new (CORRECT!!) formulas using the rule from step two.

NaCl since Na is positive 1 and Cl is minus one O2 since oxygen is a diatomic gas

So the final answer looks like this:

NaClO3 ---> NaCl + O2