What do you mean by Chemical Reaction

When we talk about chemical reactions, we have a lot of questions, such as what is a chemical reaction, what are reactants and products, and so on. Let's have a look at what a chemical reaction is;

Chemical Reaction-
Chemical reaction simply define as a reaction in which a substance (or a compound) is converted into a new one with different property. In a reaction, the substance (or a compound) which is converted into new substance (or changes their state) is called 'Reactant' and a newly formed substance is called 'Product'.  
       A chemical reaction is usually written by placing an arrow symbol between the reactants and the products. For example, if A and B are two reactants in a chemical reaction while C and D are two products, then this reaction can be represented as -
                     A   +    B      ➝     C  +   D
                   (Reactants)        (Products) 
We can also say that in a chemical reaction, reactant bonds are broken and new bond are formed in order to form a new substance. All these chemical reactions occur at different speeds. Some of these chemical reactions occur at a rapid rate while some chemical reactions take place at a slow rate. We all are seeing many Chemical reactions around us. For example- a burning of candle, burning of coal, photosynthesis, cooking, digestion, explosions, color changes, rusting of iron, formation of water molecule, CO, CO2 etc. All these chemical reactions occur at different speeds. Some of these chemical reactions occur at a rapid rate while some chemical reactions take place at a slow rate. 
For Example
Other examples are;
(1) Fast chemical reactions are, 
        BaCl₂ + H₂SO₄ ➝ BaSO₄ + 2HCl ↓ 
                2Mg + O₂ ➝ 2MgO
         Na-OH + HCl ➝ Na-Cl + H₂O
        Ag-NO₃ + Na-Cl ➝ Ag-Cl↓ + NaNO₃
(2) Slow chemical reactions are,
        2KClO₃ ➝ 2KCl + 3O₂
        4Fe + 3O₂ + x.H₂O ➝ 2Fe₂O₃.xH₂O 
       C₆H₁₂O₆ ➝ 2C₂H₅OH + 2CO₂↑
"The branch of physicochemical under which the rate of chemical reactions, mechanism of reaction, etc. is studied is called chemical kinetics".

Points to be remember
➛ One more thing is that when a chemical reaction occurs then some 'Physical' and 'Chemical changes' occur within the reactant molecule to form a new substance. Sometimes only physical properties are changing and sometimes only chemical properties are changing or sometimes both the physical and chemical changes happened simultaneously. 
➛ Therefore, it is important to have a knowledge about these changes occur in the properties of a substances. So, let us take examples to know about these changes- Folding paper is an example of physical change in which only the shape of the paper changes and its chemical property remain unchanged. Similarly melting of ice, boiling water, breaking glass,etc are an examples of physical changes. 
➛ While in a chemical change, reaction is going on, means all reactants are converting into new product. Combustion is the best example for chemical change. Like- burning of woods, colour change, fireworks ,Iron rusting, burning of fossil fuel in motor vehicle, respiration in living organism, electroplating,heat production etc.
➛ For understanding both physical and Chemical changes let's take an example- a burning candle is best example in which conversion of candle into wax is a physical change while (burning candle) conversion of heat energy into light energy is a chemical change. 
➛ Generally Physical change is related to change of state while Chemical change is related to energy absorption or rejection from the substance. The number of reactant molecules taking part in a chemical reaction or new molecules formed in a reaction can be one or more than one. 
➛ One more thing to be remember is that a chemical reaction follows the "Law Of Conservation Of Mass". According to law of conservation of mass, atoms (or molecule) can not be created and can not be destroyed. It can only be transport from one place to another place. Therefore a new product is formed from the reactant (mass remains unchanged). 


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