Science Class 7: Physical and Chemical Changes

A physical change affects the physical properties without affecting its interior structure. Physical changes include boiling water, cutting wood, dissolving sugar in water, crumpling paper, melting an ice cube, and so on. A chemical change is a change that occurs when the internal structure of a material is altered to generate a new substance. For example, chemical changes can occur during the digestion of food, the burning of wood, the baking of a cake, the curdling of milk, the mixing of acid, the boiling of an egg, the rusting of iron, and so on.

Key Terms and Facts

• Changes in any substance occur due to various internal and external influences.
• Physical as well as chemical processes are two types of changes that occur around us.
• Physical changes are the changes to a substance’s physical attributes, such as form, size, shape, and states. These alterations result in the formation of no new compounds. These modifications might as well be reversible. 
• A phase change is regarded as a change in the form of matter, often known as a physical change.
• Liquid water turning to solid ice or going through evaporation to form water, the gaseous state of water, are both examples of physical changes.
• Boiling as well as evaporation are examples of phase transitions.
• Chemical changes are the changes that alter the chemistry including composition or structure of a substance.
• Several new chemicals are produced during chemical reactions, for instance, rusting, ozone generation in the environment, etc.
• A chemical change might accompany heating, light or gas emissions, sound creation, a transition in smell or colour, etc., in the form of new products.
• If we want to extract a metal from an ore, like iron from iron ore, we must undergo a chemical transformation sequence. Likewise, medicine is the result of a series of chemical processes. Chemical reactions provide essential new substances such as polymers and cleansers.

Rusting

When the molecules of one or perhaps more compounds are reorganised, a chemical reaction occurs, resulting in one or even more new compounds. Rusting is an example of a chemical reaction. When iron is subjected to air, it develops a reddish-brown material called rust, and the process is known as rusting. Rusting is accelerated by the presence of moist air as well as seawater. We can use the following equation to illustrate rusting:

Iron (Fe) + Oxygen (O2, from the air) + Water (H2O) → Rust (Iron oxide, Fe2O3)

Rusting Prevention:

The process of preventing iron objects from being exposed to oxygen, water, or both, is known as the prevention of rust.

Mentioned below are a few ways to prevent rusting:

• Applying a layer of paint or lubricant is one of the most common ways to do it.
• Adding a metal coating to iron, such as chromium or zinc.
• Galvanization is the process of putting a coating of zinc on iron.
• The atmosphere’s ozone layer shields humans from the dangerous ultraviolet (UV) rays. Natural chemical processes involving UV light produce ozone.

Difference Between Physical and Chemical Changes

The difference between the physical and chemical changes are as follows:

Conclusion

Every day, we witness several changes including physical and chemical changes. A physical change is a change in a material’s physical qualities. Material’s physical attributes include its size, form, colour, and state of matter. Because no new substance is generated, physical alterations are typically reversible. It is the same material, but its physical qualities have altered. A chemical change is defined as forming one or more new compounds. Typically, a chemical change comprises a chemical reaction that results in new products. Examples of chemical changes include iron rusting and wood burning. The rusting of iron occurs when iron comes in contact with the oxygen and moisture or water in the atmosphere. We can prevent rusting of iron by coating the iron surface with paint or grease.