Physical and chemical changes occuring in the same process:
Indeed, both physical and chemical changes can take place simultaneously in the same process. It occurs when a process includes alterations in physical properties (such as form, state, or size) and changes in chemical properties (resulting in the formation of new substances).
The burning candle undergoes both physical and chemical changes. A physical change influences the look or shape, whereas a chemical change modifies the substance itself.
Burning of a candle
i. As the candle heats up, the hard wax begins to transform into liquid. This transformation is similar to the candle changing its appearance; it looks different (from solid to liquid), yet it remains the same wax. There is no formation of a new substance, and this is an example of physical change.
ii. The wick of the candle ignites and starts to consume the wax vapour. The wax interacts with oxygen in the air, transforming into carbon dioxide and water vapour and resulting in the formation of a new substance, and this is a chemical change.
Hence, on lighting the wick, the candle starts to melt because it absorbs heat from the wick (chemical change), making the candle wax melt (physical change).
Reversible change:
A reversible change refers to a transformation that returns to its original substance or condition. There is no formation of a new substance. Typically involves physical changes.
The changes, which allow the objects to return to its original shape and size, are reversible.
Example:
Freezing of water, melting of ice, stretching of a rubber band, blowing a balloon, and folding a paper.
Blowing a balloon
1. Blow a balloon in such a way that it does not burst. There is a change in the shape and size of the balloon when air blows into it. Now, when the air is allowed to escape from the balloon, it turns to its original shape and size.
Making paper cup
2. Making a toy ship by folding a sheet of paper. When we unfold the paper again, it comes to its original shape.
Making shapes with dough
3. Likewise, dough is made into a ball and rolled out into a roti. If its shape is not good, it can be changed back into a ball of dough again.
In all the above examples, the substance changes into its original shape and size.
In all the above examples, the substance changes into its original shape and size.
Irreversible change:
An irreversible change refers to a transformation that is irreversible, resulting in the formation of a new substance. Unable to revert to the initial state. Frequently involves chemical transformations.
The changes are irreversible, preventing them from reverting to their original shape and size, and are termed irreversible changes.
Example:
Burning of a candle, rusting of iron, burning of paper
This type of change is permanent and cannot be undone by any means. A new substance is formed in this type of change.
Bursting a balloon
1. Bursting a balloon: If a balloon is blown to its full size and pricked with the pointed tip of a pencil or needle, it cannot regain its original form.
2. Cutting a paper: On a sheet of paper, the shape of an aeroplane is drawn and cut along its outline.
2. Cutting a paper: On a sheet of paper, the shape of an aeroplane is drawn and cut along its outline.
3. Baking a roti: While making roti from dough, bringing back the dough from the roti is not possible. The change is irreversible.
Baking a roti
Desirable change:
Various beneficial changes take place in our everyday lives. A desirable change brings us benefits, advantages, or value. We strive for these changes since they enhance our lives in various ways. A change that we appreciate and that gives us positive outcomes is known as a desirable change.
The changes that are beneficial for us and the environment are known as desirable changes.
Desirable changes
Example:
Preparation of curd, manure from cow dung and dead plants, ripening of fruits, seasonal changes, germination of seeds, baking of cake and cooking food
Undesirable change:
An undesirable change refers to a shift that is unhelpful, unwanted, harmful or potentially damaging. These are the changes we prefer to avoid, as they can cause damage, ruin things, or create issues in everyday life.
The changes that are harmful to us and the environment are known as undesirable changes.
Undesirable changes
Example:
The burning of a factory, rotting of foodstuff, volcanic eruption, flood, earthquake and rusting of iron articles
Note:
i. A change may be beneficial at one moment but unfavourable at another. The burning of fuel (such as wood or coal) to generate heat is the desired change. When a house or a factory is burnt, it causes an undesired change.
ii. For some, a change may be beneficial, but it may be destructive for others. Cutting trees may be desirable for those who require wood, but it is undesirable for animals and the environment, as it disrupts the natural balance.
Have you ever experinced hiking in the mountains or hills and noticed a pile of gravel, sand, or broken rocks at the base of the slopes? These accumulations are known as sediments.
Sediments of broken rocks
They are the product of a slow natural process that has been going on for thousands or even millions of years; they did not form all at once. It occurs gradually over a period. Some slow natural changes are as follows:
- Weathering of rocks
- Soil erosion
In this theory, we will be discussing about the slow natural changes.
1. Weathering of rocks:
Imagine a vast, huge rock on a mountain. Over the years, that rock endures extreme conditions, including the hot sun during the day, cold nights, rain, wind, and even plants attempting to grow in its cracks. These natural elements slowly break the rock over time.
The two main ways of weathering of rocks are,
i. Physical change:
At times, the changes are physical. Imagine rainwater penetrating small cracks in the rock. When temperatures drop and that water freezes, it expands like the ice in a tray. This expansion creates pressure on the rock, causing the cracks to widen and slowly break the rock.
Growth of plants on rocks
Even the roots of plants can infiltrate these cracks, and as they thicken, they push the rock apart even more. Over many years, these processes can break large rocks down into pebbles and sand.
ii. Chemical change:
In some cases, the changes are chemical in nature. Rainwater is not simply pure water; it can contain small quantities of acids or various chemicals. When this water comes into contact with specific rocks, it interacts with the minerals present in the rocks.
Weathering of rocks
Basalt is a type of rock that contains iron. When exposed to air and moisture, it undergoes rusting, appearing as a red-brown coating.
2. Soil erosion:
Have you ever gathered a handful of soft, fine sand from a riverbank or discovered smooth stones in a lake? Have you considered the origins of all this loose material?
It all begins high in the hills and mountains, where rocks and soil are exposed to natural elements. When the wind blows or rain pours, these natural forces gradually disintegrate large rocks and soil into smaller fragments.
Landslide
As rainwater runs downhill, it carries small rocks, soil, and even pebbles along with it. A similar process occurs when strong winds blow across dry land. This process is known as erosion; it is a slow process.
Natural forces carry soil and small rocks from one spot to another. For instance, during a landslide, large quantities of rock and soil can slide down together. That’s a striking illustration of physical soil erosion in action and irreversible.
Reference:
https://commons.wikimedia.org/wiki/File:Landslide_between_Ye_and_Dawei.jpg
https://pixnio.com/media/aspen-forest-forest-trail-rocks-stones
https://www.pexels.com/photo/barren-rocks-and-plants-17461981/