Changes And Its Classification: What happens when a paper is folded? The shape changes, and we can get the original shape of the paper back by just unfolding it. But can we get the same paper back when it is burned? No!! But why is it so? This is because when a paper is burnt, a change in the chemical composition of the paper takes place, whereas when a paper is folded, no such changes happen. Read on to explore more about changes in this article.

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What is a Change?

A change is the transition of any substance from one form to another. Changes are part and parcel of our lives. They take place simultaneously and continuously around us. Growth in living beings, cooking of food, rusting of iron, curdling of milk, changes in weather are some common changes that we see around us.

Classification of Changes

The changes that take place around us can be classified as follows:

1. Physical and chemical changes
2. Reversible and irreversible changes
3. Slow and fast changes
4. Useful and harmful changes
5. Natural and man-made changes
6. Periodic and non-periodic changes
7. Controlled and uncontrolled changes

Physical and Chemical Changes

Physical change: A physical change is a change that does not cause a substance to become a fundamentally different substance. This means no new substances are formed in this change. Cutting, tearing, grinding, mixing are the types of physical changes that cause a change in the form of the substance but not in the composition of a material.

Phase changes are also physical changes that occur when substances undergo melting,zing, boiling, condensation, sublimation, or deposition. These changes do not cause any change in the nature of the substance.

Chemical Change: A chemical change is a change that changes the chemical composition of a substance to become a fundamentally different substance. This means new substances are formed in this change.

These changes are undertaken by chemical reactions in which the participating ingredients of the reaction are known as the reactants, and the end results are called the products. The change from reactants to products is denoted by an arrow:

Reactants → Products

Formation of a precipitate, colour change, evolution of a gas, release of odour is all indicators of a chemical change. The formation of gas bubbles is often the result of a chemical change but not in the case of boiling, as boiling does not cause any change in the chemical composition of the substance, hence is a physical change.

Burning, fermentation, rotting, cooking, rusting are all types of chemical changes because they alter the chemical composition of the original substance to produce new chemical compounds. For example, the fermentation of yeast produces alcohol and sugar; burned wood becomes ash, carbon dioxide, and water. While boiling an egg, the heat changes the interactions and shapes of the proteins in the egg white, thereby changing its molecular structure and converting the egg white from translucent to opaque.

The best way to determine whether a change is physical or chemical is to perform chemical analyses, such as mass spectroscopy, on the substance to determine its composition before and after a reaction.

Reversible and Irreversible Changes

Reversible Change:  A reversible change is a temporary change in which the original substance can be obtained by reversing the reaction conditions. These changes are observed in the size, shape and physical state of the substance. In a reversible change, no new substance is formed.
Examples: Melting,zing, evaporation, condensation, etc., are all examples of reversible changes.
Almost all physical changes are reversible in nature.

Irreversible Change:  An irreversible change is a permanent change in which the original substance cannot be obtained by reversing the reaction conditions. An irreversible change causes a change in the chemical composition of the original substance that results in the formation of new substances.
Examples: The baking of a cake is an irreversible change because once the cake has been baked, we cannot get the batter back.

Cooking is another example that undergoes chemical change as we cannot get back the raw materials that we originally started. Similarly, on mixing vinegar with sodium bicarbonate, the evolution of carbon dioxide gas in the form of bubbles takes place. We cannot get back the original substances, hence is a chemical change.

Physical changes can be irreversible too. When a wood log is ground into sawdust, that change is irreversible since the sawdust cannot be reconstituted into the same piece of wood that it was before.

Cutting grass or pulverising a rock are examples of irreversible physical changes. Firewood also represents an irreversible physical change since the pieces cannot be put back together to form the tree.

Fast and Slow Changes

Fast changes: A fast change is a change that takes place rapidly in a very short period of time. Bursting of crackers, glowing of a bulb, burning of a paper are all fast changes.

Slow change: The changes – like the growth of a child into an adult, germination of a seed to a plant, the rusting of iron – take place very slowly and a long time to occur. Such changes that take a long time to occur are called slow changes. 

Useful and Harmful Changes

Useful changes: The changes that are desirable are called useful changes or desirable changes.
The decay of cow dung and leaves to form manure, formation of curd from milk, ripening of fruit, germination of seed etc., are all examples of useful or desirable changes.

Harmful changes

However, there are some changes that are useless and undesirable and can cause us harm. Such changes are called harmful or undesirable changes.
Examples: Spoiling of food, souring of milk, rusting of iron, a forest fire, breaking off a windowpane are harmful or undesirable changes.

Many desirable or useful changes are accompanied by undesirable or harmful changes that result in the overall change becoming harmful or undesirable.
For example, the production of power in a thermal power plant is a useful and desirable change, but the simultaneous emission of smoke and other harmful gases into the environment is a harmful or undesirable change. So the overall production of power in a thermal power plant becomes an undesirable or harmful change.

Natural and Man-Made Changes

The changes that occur naturally on their own are called natural changes.
The occurrence of day and night, changes in the seasons, earthquakes, ripening of fruit, rainfall, etc., are all examples of natural changes.

However, changes that are caused due to human activities are called man-made changes. These changes include air pollution, burning of fossil fuels, deforestation, water pollution, etc. The man-made changes disturb the natural balance of greenhouse gases and have a global impact. The rise in the average temperature of the earth is also a consequence of man-made changes.

Periodic and Non-Periodic Changes 

Periodic changes are the changes that are repeated at regular intervals of time. Change of seasons, sunrise and sunset, waxing and waning of the moon are all examples of periodic changes as these changes reoccur after a certain interval of time.
However, certain changes that do not repeat themselves at regular intervals of time are known as non-periodic changes.
Examples: Earthquakes, falling of leaves from trees, hailstorms are all examples of non-periodic changes.

Controlled and Uncontrolled Changes

Controlled changes
The changes that are under the control of human beings are called controlled changes.
Example: A running train, burner flame, cutting of fruits, etc.
Un-controlled changes
The changes that cannot be controlled by human beings are known as uncontrolled changes.
Example: Sunrise, thundering, raining, formation of clouds cannot be controlled by humans and hence can be categorised as uncontrolled changes.

Summary

Changes happen around us every day, be it the growth of the child, drying of leaves, boiling water or occurrence of day and night. All these are consequences of some or the other changes. Changes can be broadly classified into physical and chemical changes, which can further be classified into reversible and irreversible changes. Most chemical changes are irreversible, whereas physical changes are mostly reversible. However, there are certain changes that can be physical and irreversible too. In this article, we learned the concept of change and its classification. We also learned the different types of changes along with some common examples.

FAQs on Changes And Its Classification

Q.1. What do you mean by change?
Ans: A change can be defined as an alteration in the physical and chemical properties of matter due to the effect of some kind of energy. Changes take place continuously. Changes in the weather, growth in living things, cooking of food, etc., are some of the common changes we see around us.

Q.2. Which property stays the same during physical and chemical changes?
Ans: Mass always remains the same, whether a substance undergoes physical change or chemical change. This is because the law of conservation of mass is valid under all circumstances. 

Q.3. What type of changes takes place in a burning candle?
Ans: When a candle burns, wax melts which is a physical change. The flame gives off \({\text{C}}{{\text{O}}_2}\) Soot, light and heat, which is a chemical change. Hence, the burning of a candle is a physical as well as a chemical change.

Q.4. What type of change takes place in the interconversion of states?
Ans: The interconversion of states is a physical change as there is no change in the chemical composition of matter.

Q.5. Dissolving sugar in water is a chemical change. True or false.
Ans: When sugar is dissolved in water, a physical change occurs because sugar molecules are dispersed within the water, but the chemical structure of the individual sugar molecules remains unchanged.

Q.6. In which type of change, alteration takes place only in specific property of matter but not in the composition?
Ans: Physical changes are those types of changes where the form of a chemical substance is affected, but not its chemical composition. For example, when the ice melts, there occurs a physical change from solid to liquid, but the chemical composition of the water molecule is the same in the solid phase as well as in the liquid phase. 

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