A decomposition reaction occurs when a compound is broken into smaller parts. This reaction can be either thermal decomposition or electrolytic decomposition or light decomposition.
For example, when calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide
COMBINATION REACTION OR SYNTHESIS REACTION:
As the name suggests, in Combination reaction, two or more substances combine to form a new substance or single product.
For example, Hydrogen burns in oxygen to form water:
A chemical equation in which the number of atoms of all the molecules is equal on both sides of the equation is known as balanced chemical equation.
An unbalanced chemical equation has unequal masses of various elements in reactant and product.
In light decomposition, the compound decomposes due to exposure to light
DISPLACEMENT REACTION OR SUBSTITUTION REACTION:
In Displacement reaction, an atom or group of atoms in a molecule is replaced by another atom or group of atoms to produce new substances.
A more reactive element displaces a less reactive element from its aqueous salt solution.
DOUBLE DISPLACEMENT REACTION OR METATHESIS REACTION
The reaction where two reacting molecules exchange their partner ions in solution is called double displacement reaction.
This occurs when a strip of zinc metal is placed in copper sulphate solution to produce zinc sulphate solution and copper.
Likewise, when silver nitrate solution is added to sodium chloride solution, it results in the formation of white precipitate of silver chloride along with sodium nitrate solution:
Similarly, when an aqueous solution of NaCl is added to an aqueous solution of AgNO3, the compounds break down into hydrated Na+ and Cl– ions and Ag+ and NO-3 ions.
When combined, a double displacement reaction takes place. A soluble compound NaNO3 and an insoluble compound AgCl are formed. This happens when Ag+and Cl– ions combine in the vessel, and a white solid precipitate is formed. As the solid precipitates, the Na+ and NO-3 ions remain in solution. Thus, we have the following balanced equation:
It occurs between an acid and a base forming of salt and water.
Dissociation reaction takes place, when a substance breaks up into its ions.
Formation of insoluble salts results in the precipitation reaction.
Although the reactants are soluble, the product formed would be insoluble. It separates out as a solid.
A precipitation reaction occurs when a solution which originally contains dissolved substances, produces a solid.
The solid is generally denser and settles at the bottom of the vessel in which the reaction takes place.
A chemical equation adequately describes reaction in solutions.
But the typical molecular equation has different representations for reactions of ionic compounds in aqueous solution (water).
It may indicate formulas of reactants and products that are not present, and eliminate completely the formulas of the ions that are the real reactants and products.
Ionic equation results if the substance in the molecular equation that are actually present as dissociated ions are written in the form of their ions.
When lead nitrate reacts with potassium Iodide, a yellow precipitate of lead Iodide and a by-product of potassium nitrate is formed.