Is Matter Around us Pure?

06 Physical and Chemical Changes

Physical properties of matter are its appearance and observable properties like color, odor, taste, solubility, rigidity, fluidity, melting and boiling points, etc.
Chemical property is a property exhibited during a chemical reaction like pH, reactivity, inflammability, etc.

Those changes, in which no new substances are formed, are called physical changes.
Due to physical changes, observable changes occur in matter.
Neither the composition nor the chemical nature of matter is changed but, molecules rearrange themselves without affecting the internal composition.
In short, physical change doesn’t affect the chemical property.
The physical changes are temporary changes which can be reversed easily to form the original substance.
For example, although ice, water and water vapour all look different and display different physical properties, they are chemical
ly the same.
Other examples are whipping egg albumin, crushing of tomato, breaking of a bar magnet, etc.

Substances vary in chemical properties according to which substances show variation in their reactivity.
Those changes in which new substances are formed, are called chemical changes.
It is commonly known as a chemical reaction that results in a new product.
The chemical changes are permanent changes which are usually irreversible.
Existing bonds between the molecules break and the composition of the substance change due to making of new bonds.
For example, heating of a magnesium wire in air forms a white powder called ‘magnesium oxide’. This magnesium oxide is an entirely new substance. Thus, a new chemical substance is formed during the burning of a magnesium metal wire. So, the burning of a magnesium wire is a chemical change.
Some other examples of chemical changes are burning of paper, formation of curd from milk, rottening of fruits and cooking of food, combustion, rusting, fermentation, etc.

Comparison of physical and chemical changes:

Physical change	Chemical change
No new substance is formed in a physical change.	A new substance is formed in a chemical change.
A physical change is a temporary change	A chemical change is a permanent change.
A physical change is easily reversible.	A chemical change is usually irreversible.
Very little heat or light energy is usually absorbed or given out in a physical change.	A lot of heat or light energy is absorbed or given out in a chemical change.
The mass of a substance does not alter in a physical change.	The mass of a substance does alter in a chemical change.