Chemical Reactions

Back Home Next

Decomposition Reactions

Decomposition Reaction Video

When a single reactant breaks apart to form 
General form



H2CO3(aq) → H2O(l) + CO2(g)

Thermal Decomposition

Some substances will only decompose when heated to.


--> +

Just 100g of NaN3 can produce litres of nitrogen gas in seconds.  This is used in

Combination (Composition) Reactions

Combination Reactions Video

When two or more reactants combine to form
General Form
X + Y -->

H2(g) + Cl2(g) → 2HCl(g)



Displacement Reactions

Replacement Reactions Video Part A Replacment Reactions Video Part B

Precipitation Reactions

Precipitation Reaction Video

This occurs when two clear liquid solutions are added and a appears and falls to the bottom of the solution.

Eg Lead Nitrate (aq) and Potassium Iodide (aq) --> Potassium Nitrate (aq) + Lead Iodide (s)

Precipitation Reactions and Solubility

A precipitation occurs when a substance will not dissolve (usually in water) and it is called .

Sugar is where as Chalk is in water.

Solubility is realted to the ability of ionic compounds (eg NaCl – salt) to break apart into its eg Na+ + Cl- when dissolved in water.


Ionic Compounds

Substances made up of a lattice (or crystal) structure. The substances have a positive ion called a and a negative ion called an .
There are normally , and brightly coloured.

The cations are atoms (or compounds) that have lost and the anions are atoms (or compounds) that have gained .





Predicting Precipitates

Scientists use a list of solubility rules to help them predict if something will dissolve or not

From the table predict which of the products will be a precipitate
KCl(aq) + AgNO3(aq) → KNO3() + AgCl()