Chemical Reaction

A chemical reaction is a process in which a chemical transformation takes place of one set of chemical

substances to another. This may combine two or more substances to single substance or vice versa. The substances before transformation are called reactants and substance formed after transformation are called products. There are four major types of chemical reactions as listed below

1. Combination reaction: In this reaction two or more substances combine to form a single substance. For example

2H₂ + O₂ → 2H₂O

2K + Cl₂ → 2KCl

N₂ + 3H₂ → 2NH₃

4Fe + 3O₂ → 2Fe₂O₃

2. Decomposition Reaction: In this reaction single substance breaks down to two or more substances. For example

CaCO₃ → CaO + CO₂

NH₄OH → NH₃ + H₂O

2KClO₃ → 2KCl + 3O₂

3. Displacement reaction: Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Both metals and non-metals take part in displacement reactions. Foe examples

2K + 2HCl → 2KCl + H₂

Ca + H₂SO₄ → CaSO₄ + H₂

Zn + H₂SO₄ → ZnSO₄ + H₂

NaCl + AgNO₃ → NaNo₃ + AgCl

4. Acid-Base Reaction: The chemical reaction between acid and base is called acid-base reaction. In almost cases the products are salt and water.for examples

HCl + NaOH → NaCl + H₂O

HNO₃ + KOH → KNO₃ + H₂O

2HCl + CaO → CaCl₂ + H₂O

H₂SO₄ + FeO → FeSO₄ + H₂O

Factors affecting chemical reaction:

1. Temperature: Generally increase of temperature causes increase in rate of chemical reaction because increase of temperature causes increase in internal kinetic energy of reactants and collision process becomes faster.
2. Pressure: In general increase in pressure causes increase in rate of chemical reaction especially in case of gases.
3. Area of contact: Area of contact between reacting substances increases rate of chemical reaction.
4. Light: Some silver compounds react in presence of light. Photosynthesis takes place in presence of light.
5. Catalyst: The substance which increases the rate of reaction is called catalyst. In many reactions catalyst play key role. For example hydrogen peroxide decomposes by catalyst manganese dioxide.
6. Concentration of solution: Increase of concentration of reactant solution generally increases rate of chemical reaction.

Endothermic reaction: The chemical reaction which takes place by absorbing heat is called endothermic reaction. For example, production of Lime from limestone.

CaCO₃ → CaO + CO₂
Exothermic Reaction: The chemical reaction in which heat is released is called exothermic reaction. For example reaction of quick lime with water.

CaO + H₂O → Ca(OH)₂ + Heat