CR_Decomposition Reactions Lesson

Decomposition Reactions

Remember that decomposition reactions are just the opposite of synthesis reactions. So, since you have already learned the types of synthesis reactions, all you need to do is reverse them and you have the decomposition reaction.

Let's start by reviewing the five types of synthesis reactions in this game below. 

Now, all we need to do is reverse these to make them into decomposition reactions!

1. Binary compounds or molecules will break down into their elements. Some oxides, when heated, decompose.

AB → A+B Examples: 2HgO(s) → 2Hg(1) + O2(g) Some decomposition reactions are produced by electricity. Examples: 2H2O) 2H2(g) + O2(g) 2NaCl (1) 2Na(s) + Cl2(g)

2. Metallic carbonates, when heated, break down to the oxide and carbon dioxide.

MCO3 MO + CO2 → (M represents any metal. You would need to apply charge of that metal when writing the formula.) Example: CaCO3 → CaO + CO2

3. Chlorates (ClO3-), when heated, will break down to the chloride salt and oxygen.

XCIO3 → XCI + O2 (X represents any element. You would need to apply charge of that metal when writing the formula.) Example: 2KCIO3(s) 2KCI(s) + 302(g)

4. Most metallic hydroxides (bases), when heated, decompose into metallic oxides and water.

MOH → MO + H2O (M represents a metal. You would need to apply charge of that metal when writing the formulas.) Example: Ca(OH)2(s) → CaO (s) + H2O(g)

5. Some acids, when heated, decompose into nonmetallic oxides and water.

Acid (NM)O + H2O (NM represents a non-metal. You would need to apply charge of that metal when writing the formulas.) Example: H2SO4 → H2O(l) + SO3(g)

Other Decomposition Reactions

Not all decomposition reactions fit neatly into the categories we have discussed. Here are some fairly common reactions that don't fit one of our examples:

When ammonium carbonate is heated, ammonia, carbon dioxide, and water are formed:

LaTeX: (NH_4)_2 CO_3 \rightarrow 2NH_3 + CO_2+H_2O

When hydrogen peroxide is placed in light, it decomposes to water and oxygen:

LaTeX: 2H_2O_2 \rightarrow 2H_2O + O_2

When a hydrate, such as copper II sulfate pentahydrate is heated, the water and salt separate:

LaTeX: CuSO_4 \cdot 5H_2O \rightarrow CuSO_4+H_2O

Remember to work on the module practice problems as you complete each section of content.

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