Properties of Chemical Reactions: A chemical reaction is a conversion of one or more chemicals (the reactants) into one or more distinct compounds (the products). Chemical elements or chemical compounds make up substances. In a chemical reaction, the atoms that constitute the reactants are rearranged to produce various products.

Technology, society, and even life itself depend on chemical reactions in one way or another. Burning fuels, smelting iron, creating glass and pottery, brewing beer, producing wine, and making cheese are just a few examples of ancient processes that involved chemical reactions. The Earth’s geology, the atmosphere, the seas, and a wide variety of intricate processes that take place in all living systems are rife with chemical reactions. Continue reading the article to know more details on the Properties of Chemical Reactions.

What are the Characteristics of a Chemical Reaction

The following are the Characteristics of a Chemical Reaction:

• Formation of Precipitate
• Change in Colour
• Evolution of Gas
• Change in State
• Change in Temperature or Evolution/Absorption of Heat
• Sound and Light May Be Produced
• Change in Smell or a New Smell Can Be Given Off

Formation of Precipitate 
A precipitate is a solid, insoluble product which separates from the solution during the reaction and characterises a chemical reaction.

Change in Colour
When an apple cuts into pieces and keeps it away for some time, it acquires brown colour. Similar observations can be seen in the case of potatoes and brinjals.

Evolution of Gas and Change in Temperature
(A) Evolution of a gas and exothermic reaction 
Reactions which produce heat are called exothermic reactions. The evolution of a gas and liberation of heat characterise a chemical reaction.

Other Examples of Exothermic Reactions

•  Burning of natural gas
  CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2 H₂O (g) + heat
• Respiration is an exothermic reaction where glucose (food breaks into simpler substances such as carbohydrates, which further breaks into glucose during digestion of food) combines with oxygen in the cells of our body and releases energy to work and play.
  (C₆H₁₂O₆) + 6O₂ → 6CO₂ + 6H₂O (l) + heat
  Glucose
• The decomposition of vegetable matter into compost is also an exothermic reaction.

(B) Endothermic reaction

Such reactions which absorb heat during the reaction are called endothermic reactions. The absorption of heat characterizes a chemical reaction. Another example of an endothermic reaction is photosynthesis.

Change in State
When a wax candle is burned, its wax (solid) changes into carbon dioxide (gas) and water vapour (gas). Such chemical reactions can be identified by a change in state (here, solid to gas) and by the formation of one or more new substances.

Sound and Light May Be Produced
The explosion of fireworks produces heat, light, sound and unpleasant gases that characterise chemical reactions.

Change in Smell or New Smell May Be Given Off
It happens when food is spoiled, formation of curd from milk, souring of curd, cooking of food, fermentation of grapes, etc.

Types of Chemical Reactions

The following are the different types of Chemical Reactions:

Combustion Reaction: A reaction with a combustible material with an oxidizer to give an oxidised product is known as Combustion Reaction. An oxidiser is a chemical a fuel requires to burn (generally oxygen).

Decomposition Reaction: A reaction in which a single component breaks down into multiple products is known as Decomposition Reaction. Certain changes in energy in the environment have to be made like heat, light or electricity breaking bonds of the compound.

Neutralisation Reaction: A reaction between an acid and a base giving salt and water as the products is known as Neutralisation Reaction. The overall pH of the products when a strong acid and a strong base undergo a neutralisation reaction will be 7. The water molecule formed is by the combination of OH– ions and H+ ions.

Precipitation or Double-Displacement Reaction: A displacement reaction in which two compounds react and consequently, their anions and cations switch places, forming two new products, is known as Precipitation or Double-Displacement Reaction.

Synthesis Reaction: One of the most basic types of reaction wherein multiple simple compounds combine under certain physical conditions giving out a complex product, is known as Synthesis Reaction. The product will always be a compound.

Redox Reaction: A reaction in which there is a transfer of electrons between chemical species is known as a REDuction-OXidation reaction.

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