7.7 DECOMPOSITION REACTIONS

By: Jason Kahan, Melissa Marini, and Jake Marrazzo

When a substance is heated it decomposes into two simpler compounds. Many compounds break apart or decompose with the addition of energy.

A chemical decomposition reaction or analysis reaction is one of the most common types of chemical reactions

A WAY TO REMEMBER Essentially, decomposition reactions

are the opposite of combination reactions. A compound decomposes (i.e.,"splits-up") into two or more compounds and/or elements. For example mercury(II) oxide will, upon heating, decompose into mercury metal and oxygen:

In a decomposition reaction a single compound is broken down into two or more products. These products can be any combination of elements and compounds.

3 RULES TO REMEMBER

1) All binary compounds will break down into their elements.

2) All carbonates break down to the oxide and carbon dioxide.

3. Chlorates (like KClO3 and Ba(ClO3)2 )will break down to the binary salt and oxygen.

Examples of Decomposition:

HgO ---> Hg + O2

H2O ---> H2 + O2

FeS ---> Fe + SCaCO3 ---> CaO + CO2

Na2CO3 ---> Na2O + CO2

It is usually very difficult to predict the products of decomposition reactions. When a simple binary compound breaks down, however you know the products will be the constituent elements

A. Mg2+Cl2

B. Mg+Cl

C. Mg+Cl2

D. M+G+C+L

What would MgCl2 break down into?

Most decomposition reactions require energy in the form of heat, light, or electricity.

2H2O(l) electricity H2(g) + O2 (g)

What is the energy that causes the decomposition reaction in the problem above?

A. heat

B. Mr. sweeten

C. fire

D. Electricity

PRACTICE PROBLEMS

Break down:

1. barium carbonate

2. magnesium carbonate

3. potassium chlorate

THE END