Physical Changes of Matter is an important phenomenon that takes place in nature. The world around us is full of different types of substances that are always changing. Various types of phenomenon such as cycle of day and night, weather etc always undergoes changes.Changes are a part of our life. For example - A baby grows into an adult undergoing a lot of changes.
What is the definition of a change?
An alteration in chemical and physical properties of matter that gives it new properties is known as a change.
How are the changes classified?
Changes are classified as follows -
1. Natural Changes - The changes that occur by nature are known as natural changes. For example - Growth of plants, animals, human beings etc.
2. Man - made changes - The changes that are caused by man are known as man-made changes. For example - Making of food, making of furniture, painting houses etc.
3. Period and Non-Periodic changes -
* Periodic Changes - The changes that take place after a definite or fixed period of time are known as periodic changes.For example - Phenomenon of day and night, change of seasons etc.
* Non-Periodic changes - The changes that may occur at any time are known as non-periodic changes. For example - Breaking of glass, Tearing of paper etc.
4. Desirable and Undesirable Changes
(a) Desirable Changes - The changes that are useful are known as desirable changes. For example - Drying of clothes, ripening of fruits etc.
(b) Undesirable Changes - The changes that are harmful for us are known as undesirable changes. For example - Rusting of iron, spoiling of food, rottening of fruits,damaging of houses, floods, earthquakes etc.
5. Fast and Slow Changes
(a) Fast Changes - The changes that take place in a short period of time are known as fast changes. For example - breaking of a vase,blinking of eyes,bursting of an inflated balloon,burning of paper etc.
(b) Slow Changes - The changes that take place in a long period of time are known as slow changes. For example - formation of curd,germination of a seed,formation of fossil fuels etc.
6. Reversible and Irreversible Changes
(a) Reversible Changes - The changes after which the substance can be brought back into its original form are known as reversible changes. For example - changing of water into ice, moulding of clay etc.
(b) Irreversible Changes - The changes after which the substance can't be brought back into its original form are known as irreversible changes. For example - cooking of food, growth of a plant etc.
The changes mentioned above can be divided into two groups. These are -
7. Physical and Chemical Changes
(a) Physical Changes - The change in which any new substance is not formed and the chemical composition of the substance doesn't change is known as a physical change. It is a temporary change. Some of its physical properties may change such as colour, shape, size etc. For example - When ice changes into water, there is only a change in the physical properties while the chemical properties of both remain the same. Any new substance is not formed only there occurs a change in the state of the substance.
∆
Ice ➡ Water
What are the characteristics of physical change?
The characteristics of physical changes in matter are -
1. Any new substance is not formed.
2. The change is reversible and temporary.
3. The chemical properties of the substance are not changed.
4. There may occur a change in shape, colour or size.
Another example is changing of water into steam.
∆
Water ➡ Steam
Some other examples are freezing,melting, boiling, evaporation, boiling, condensation, sublimation, dissolving salt in water .Some more examples of physical changes are -
* Tearing of paper - On tearing a piece of paper, there is no difference the properties of paper and its small pieces. There only occurs a change in the size of the paper. Any new substance is not formed.
* Breaking of a glass tumbler - When a glass tumbler breaks, the properties of the glass and the glass tumbler remain same and no new substance is formed.
* Drying of wet clothes - The heat of the sun changes the water in the wet clothes into vapours due to which the clothes become dry. This is known as evaporation. Any new substance is not formed.
* Glowing of an electric bulb - The bulb starts glowing when an electric current is passed through its filament while it stops glowing when the flow of current is stopped.
* Sublimation - It is the process in which the sublime products such as ammonium chloride, camphor, iodine etc change into vapours on heating. These vapours change back into solid on cooling.
Camphor ➡Vapours ( Camphor)
* Evaporation - The process in which the liquid changes into its vapours below its boiling point is known as evaporation. This process is slow and takes place at all temperatures.
The rate of evaporation depends upon the following factors -
* Nature of liquids - Volatile liquids such as petrol, alcohol, nail polish remover etc evaporates quickly while non-volatile liquids such as water, oil, juice etc evaporates slowly.
* Temperature - An increase in temperature increases the rate of evaporation.
* Humidity - The rate of evaporation decreases with increase in humidity.
* Surface area of liquid - An increase in surface area of the liquid increases the rate of evaporation.
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