Chemical Reactions

The process of transformation of chemical substance to another is known as chemical reaction.

A chemical change involves the formation and cleavage of chemical bonds between atoms. Any chemical change can be described by using a chemical equation which gives complete idea about conversion of molecules during reaction.

Let’s elaborate; what is a Chemical reaction. It can define as change in bonding of reacting molecule to form new chemical compound by the formation of new chemical bonds.

The chemical substances take part in chemical reactions is called as reactant and newly formed substances are known as products. A chemical change can complete in one step or multi steps which can be described by using reaction mechanism. Chemical equation is the graphical representation of such a reaction which provides direction of reaction, physical states of reactant and products and the number of molecules taken part in reaction.

Different Types of Chemical Reactions and examples are as follow;

1. Combustion: Oxygen combines with substance to form carbon dioxide and water with a large amount of heat.

CH₄+ 2 O₂  CO₂ + 2H₂O

2. Synthesis: two or more chemical substance combines to form a more complicated one.

2Mg + O₂ 2MgO

3. Decomposition: A complex molecule decomposes in to simpler ones.

2HI  H₂ + I₂

4. Single displacement: one element trades places with another element in a compound.

Mg + 2 HClMgCl₂ + H₂

5. Double displacement: The anions and cations of two different molecules interchange and form two entirely different compounds.

BaCl₂ + H₂SO₄  BaSO₄ + 2HCl

6. Neutralization: A double displacement reaction between acid and base to form salt and water.

HCl + NaOH  NaCl + H₂O

There are a many observations which indicate a chemical change has occurred. These are called as Signs of a Chemical changes. Like; the formation of a precipitate during chemical reaction is one the best sign which can observe easily. When an ionic compound reacts with other to form insoluble salt, it gets settle down at the bottom of test tube in the form of precipitate. Other signs of chemical-reactions are;

• Color change.
• Liberation or absorption of energy.
• Formation of gas.
• Change in temperature of reacting solution

Let’s perform any Chemical Reaction Experiments and observe sign of reaction.

Take 1-2 ml of a 0.1 M lead (II) nitrate solution in a test tube and add it to 1-2 ml of a 0.1 M potassium iodide solution. When lead nitrate reacts with potassium iodide it form yellow colour precipitate of lead iodide it’s an example of double displacement reaction.

Pb(NO₃)₂ + 2KI  PbI₂ + 2KNO₃

Hence color change and precipitate from colorless reactants can be observed in reaction.