Define chemical reaction. Explain its types and sub-types with example.
Define chemical reaction. Explain its types and sub-types with example.
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants.
Examples :
i. Combustion
ii. Oxidation (rusting
iii. Decomposition or fermentation
iv. Photosynthesis
v. Reacting acids and bases together.
The different types of chemical reaction are
1.Combination reaction:
In a combination reaction, two or more elements combine to form a compound or an element and a compound can combine to form a new compound .
For example: Magnesium and oxygen combine when heated to form magnesium oxide.
2Mg(s)+ O2(g) ___combination→3MgO(s)
2.Displacement reaction:
Those reactions in which one element takes the place of another element in a compound, are known as displacement reaction. In general a more reactive element displacement reaction. In general, a more reactive element displaces a less reactive element from its compound.
For example: When a strip zinc metal is placed in a copper sulphate solution, then zinc sulphate solution and copper are obtained:
CuSO4(aq)+Zn(s)→ZnSO4(aq)+Cu(s)
In this reaction zinc displaces copper from copper sulphate solution.
And the sub-types of displacement reaction are :
i) Single Displacement Reaction :
Those reactions in which one element replaces another element from its salt or compound are called single displacement reactions. These are also called single replacement reactions.
For example, potassium is more reactive than magnesium, so potassium replaces magnesium from magnesium chloride. The reaction between potassium and magnesium chloride occurs as follows :
2K + MgCl2 → 2KCl + Mg
ii) Double displacement reaction:
Those reactions in which two compounds by the exchange of ions to form two new compound are called double displacement reactions. A double displacement reaction usually occurs in solution and one of the products, being insoluble, precipitates out.
For example: When silver nitrate solution is added to sodium chloride solution, then a white precipitate of silver chloride is formed long with sodium nitrate solution :
AgNO2 (aq)+NaCl(aq)→AgCl(s)+NaNO3
In this double displacement reaction, two compounds, silver nitrate and sodium nitrate.
4. Decomposition reaction:
The reaction in which a compound decomposes to form two or more substance is called decomposition reaction.
e.g. CaCO3-------Δ-----→CaO+CO2
This type of reaction is further classified as:
a). Acid-base reaction (Neutralization reaction ): It is the process of formation of salt and water by the reaction between acid and base. Eg. KOH + HNO3 →KNO3 + H2O
b). Hydrolysis: It is the interaction of positive and negative ions of a salt with water resulting acidity or basicity in the solution. Eg. Na2CO3 + 2H2O → 2NaOH + H2CO3
c). Precipitation reaction: It is a process of formation of one of the product as an insoluble product by mixing two compounds from their aqueous solution.
Eg. AgNO3 + HCl →AgCl↓ + HNO3
d). Salt-acid displacement reaction: It is a double displacement reaction in which a salt of volatile acid interacts with non volatile acid such as Sulphuric acid to give the volatile acid . Eg. 2NaCl + H2SO4 (conc.) ---------------------> Na2SO4 + 2HCl↑
5. Oxidation and reduction reactions:
Oxidation:
1. The addition of oxygen to a substance is called oxidation.
2. The removal of hydrogen from a substance is also called oxidation.
Reduction:
1. The addition of hydrogen to a substance is called reaction.
2. The removal of oxygen from a substance is also called reduction.
From the above definitions, it is clear that the process of reduction is just opposite oxidation. Moreover, oxidation and reduction reactions occur together.
