Reversible and Irreversible Changes: Understand Differences with Examples

Reversible and Irreversible Changes: Changes are the law of nature. These are important for our life. Most of the things around us are changing all the time. We observe some common changes like weather changes, burning of paper, changes in children, and changes in plants (germination of seeds, growth, flowering, fruiting, etc.).

Every change has a cause. These causes can bring about changes in a substance’s shape, size, position, colour, or internal structure. Changes can be broadly categorised as Reversible and Irreversible changes and as Natural and Man-made changes. This article will cover Reversible and Irreversible changes in detail with definitions and reversible change examples. Read on to know more.

Classification of Changes

A substance changes to form a new substance only when certain agents like heat, light, electricity, force, etc., are applied. Now, if the agent is causing the change to be removed, then in some cases, the new substance changes the reverse direction to form the original substance. And we say that the change can be reversed or that the change is reversible. If the new substance formed does not undergo reverse change to form the original substance, then we say that change cannot be reversed, or the changes are irreversible.

In reality, some of the changes can be reversed, whereas other changes cannot be reversed. As a result, all changes in our environment can be divided into two categories: reversible and irreversible.

We will now discuss reversible changes and irreversible changes around us in detail, one by one.

Reversible Change

A change that can be reversed or we can get back its original substance (shape) is called a reversible change, e.g., stretching of a rubber band, a balloon changing its size, shape on blowing air into it, water changing into ice on cooling, wax changes into liquid on heating, etc.

Some Reversible Change Examples

i. Melting of Ice: After the ice melts, the water formed can be frozen again to get back the ice.

ii. Folding a paper or cloth: A paper or cloth can be folded back to its original form.

iii. Stretching of a rubber band: If we stretch a rubber band with the force of our hands, it undergoes a change, and its length increases but releasing the force, the rubber band comes back to its original length. This means that the change which occurred in the rubber band on stretching has been reversed on releasing. So, the stretching of a rubber band is a reversible change. Similarly, the stretching of spring is also a reversible change.

iv. Coal tar is a black solid material which is used in making a repairing road. When coal tar is heated, it melts to form a thick black liquid. The melting of coal tar on heating is a reversible change. This is because when hot molten coal tar gets cooled, it solidifies again.

v. Some other examples of reversible changes are knitting a sweater, inflation of the tire, ironing of clothes, boiling of water, melting of wax or butter, rolling a roti dough, heating of milk, etc.

The following activities can help you understand this:

Activity 1: To study the reversible change in a balloon

Take a balloon and blow it. The shape and size of the balloon have changed. The shape of the balloon comes back to its original shape when it stops squeezing it. The balloon regains its original shape and size. Therefore, it is a reversible change.

A balloon changes its size and shape by blowing air into it.

Activity 2: To show that rolling of roti of a dough is a reversible change

Take some dough (kneaded flour) and make a ball of it. The ball of the dough changes into a circular roti by using a rolling pin (belan). We can convert this rolled roti back into the ball of dough. Hence, this is a reversible change. 

Now, we observed the activities mentioned above. In these activities, one thing is common that it is possible to get back to its own and original shape with which we started.

Changes in which physical properties like shape, size, and state change without the formation of a new substance are called physical changes. They can be reversed.

Irreversible Change

A change that cannot be reversed or we cannot get back to its original state is called an irreversible change, e.g., milk changes into curd, iron changes to rust, burning of paper, cooking of food, etc.

Several irreversible changes are happening all around us. These result in a new material being produced, which may or may not be useful.

Examples of Irreversible Change

i. Ripening fruits is an irreversible change because it is not possible to get back the raw fruits from ripened or mature ones.

ii. The flower blooming is an irreversible change because flowers cannot turn back into buds.

iii. When milk is not refrigerated, it spoils quickly, especially in the summer. This is known as curdling or sour milk, and it is an irreversible process. If we want to make cottage cheese or paneer, we can curdle milk by adding lemon juice.

iv. The act of burning paper is an irreversible change. After a piece of paper is burned, a new substance known as ash is left or formed. The appearance and properties of this new substance are distinct from those of paper.

v. Cooking food causes irreversible changes because we can’t get the ingredients back to their original state after they have been cooked. For example, after a cake is baked using milk, flour, chocolate, milk, etc., we cannot get back the ingredients.

vi. Some other examples of irreversible changes are bursting of a balloon, making cheese from milk, burning of wax, breaking of glass, rock, wood, ripening of fruits or decay of plants, setting of cement, formation of curd from milk, rusting of iron, making of cake or roti, etc.

Activity 3: To show that toy (paper) aeroplane cut out of paper is an Irreversible Change.

We take the piece of paper. Draw a toy aeroplane on it and cut along its outline, as shown in the figure.

An aeroplane cut out of paper.

We see that the change which has occurred in this activity be irreversible.

Changes in which chemical properties of a substance change and new substance formed are called chemical changes. They cannot be reversed.

Difference Between Reversible and Irreversible Change

The following table provides data regarding the differences between the reversible and irreversible changes:

Summary

Changes are taking place around us all the time. Every change is happening due to some reason. This change may be temporary or permanent. Changes occur in many different ways in form, shape, size, colour, volume, etc., like milk into curd, seedling into a tree. This article learned about the classification of changes, reversible and irreversible changes, and their examples.

FAQs on Reversible and Irreversible Changes

Q.1: What are reversible and irreversible changes? Explain with examples?
Ans: Reversible change: Changes that are temporary and can be reversed by changing conditions. In this change, the products formed can be converted back into their original forms.
Example: Water can be changed into ice by placing it in thezing chamber of the fridge. The ice so formed can be converted back into the water by placing the ice outside the fridge.
Irreversible change: Changes that are permanent and cannot be reversed by changing conditions. In this change, the products formed cannot be converted back into their original forms. 
Example: When a paper is burnt, it changes to ash and smoke. From ash and smoke, we cannot get back paper. Thus, the change is irreversible.

Q.2: What is an example of irreversible change?
Ans: The act of burning paper is an irreversible change. After a piece of paper is burned, a new substance known as ash is left or formed. The appearance and properties of this new substance are distinct from those of paper.

Q.3: What are the examples of permanent and temporary change?
Ans: The examples of temporary changes are knitting a sweater, inflation of the tire, ironing of clothes, boiling water, melting of wax or butter, etc.
Examples of permanent changes are bursting of a balloon, making cheese from milk, burning of wax, breaking glass, rock, wood, ripening of fruits or decay of plants, etc.

Q.4: What is the difference between a reversible and irreversible change?
Ans: 

Q.5: Why do reversible reactions never complete?
Ans: Reversible reactions never complete because they reach equilibrium after a given amount of time. As a result, the concentration of reactants and products remains constant; it neither increases nor decreases.

Q.6: Why is the baking of a dough an irreversible change?
Ans: When you make the dough, you are only changing the shape of the dough, not the chemical structure. Thus, it’s a reversible change. Though you bake a chapati to change its chemical structure, you can’t turn it back into dough since the change is irreversible.

Practice CBSE Class 6th Questions

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