Home » Physical and Chemical Changes: Class 7 Chapter 6 Science Notes

Physical and Chemical Changes: Class 7 Chapter 6 Science Notes

by admin
Physical and Chemical Changes: Class 7 Chapter 6 Science Notes

Physical and Chemical Changes CBSE Class 7 Science Chapter 6 Revision Notes: Students of CBSE Class 7 can download the Physical and Chemical Changes Chapter 6 Notes PDF here for free. For CBSE Class 7 Science exams, this PDF will help students prepare and revise the chapter on Physical and Chemical Changes thoroughly.

NCERT Class 7 Science Chapter 6 Notes, designed by SpeEdLabs’ subject experts, are an excellent resource for students preparing for their Class 7 science exams. The Class 7 Science chapter 6 Notes PDF is available on our official website and SpeEdLabs mobile app, so students can learn at their convenience. If you want to score high marks, download NCERT Solutions PDF and refer to the questions and answers.

Physical and Chemical Changes Class 7 Science Revision Notes – Chapter 6

Physical vs. Chemical Changes

Introduction

There are several changes we come across daily e.g dissolving sugar in water, or flattening a metal rod by beating it. These involve changes in the form of the substance. Changes can be classified as:

(i) Physical

(ii) Chemical

Physical Properties

Physical properties include size, shape, colour and state (solid/liquid/gas) of a substance.

Physical Change

  •         Any change to the physical properties of a substance is called a physical change.
  •         Physical changes are usually reversible as no new substance is formed. It is the same substance but with changed physical properties.

Chemical Change

  •         A change in which one or more new substances are formed is called a chemical change.
  •         Usually a chemical change involves a chemical reaction, which forms new products.
  •         Example: Rusting of Iron, or burning wood.

Metallic Oxides

Formations of metal oxides are examples of chemical changes. They are formed by the reaction of oxygen in air.

– Burning of Magnesium ribbon:

– 2Mg + O2 2MgO

– The product formed is the oxide of magnesium, which is in the form of ash. It does not look anything like the magnesium ribbon used for burning.

Reaction of Metallic Oxides with Water

  •         Reaction of metal oxides with water form metal hydroxides.
  •         Example dissolving Magnesium oxide in water, by stirring the ash very well with water.
  •         MgO + H2O Mg(OH)2
  •         The product formed is basic in nature and turns red litmus paper blue

Reaction between Baking Soda and Vinegar

When a pinch of baking soda is added to vinegar we hear a hissing sound and observe the formation of bubbles.

– Vinegar (Acetic Acid) + Baking Soda (Sodium bicarbonate)  CO2 (Carbon dioxide) + Other products

The carbon dioxide produced during the reaction of Vinegar and baking soda, when passed through lime water gives calcium carbonate, as follows:

– CO2 + Ca(OH)2 (lime water) Calcium Carbonate (CaCO3) + H2O

– The calcium carbonate turns lime water milky.

Observations that indicate a Chemical Change

  •         Heat or light is absorbed or given out during a chemical reaction.
  •         Production of sound
  •         Production of gases or precipitates
  •         Production of smell
  •         A colour change may occur

Rusting

  •         When substances made of Iron are exposed to oxygen and moisture in the atmosphere, it forms a red layer, which is called rust.
  •         The formation of rust can be represented by the following reaction:
  •         4Fe + 3O2 2Fe2O3. The chemical formula for rust is Fe2O3.nH2O. More the moisture in the air quicker formation of rust.

Galvanization

– The process of depositing zinc on the surface of Iron to prevent rusting is called galvanisation.

– Example: Iron water pipes are galvanised. Ships are made out of iron which is galvanised. Due to the presence of salts in seawater, the process of rusting is hastened. Hence ships need to replace their iron body every year.

Crystallisation

– The process of separation of salts from their solution is called crystallisation. It is a purification technique that purifies seawater or separates crystals from impure samples. It is a physical change.

Benefits of SpeEdLabs’ Science Class 7 Physical and Chemical Changes Notes

  •         The Revision notes for Class 7 Science Chapter 6 will serve as a great reference tool for students to strengthen their understanding and revision.
  •         It will help students to become more confident during the exam about answering even the most complex questions.
  •         Using the revision notes, students can revise their chapters quickly and efficiently without sacrificing quality.
  •         As the revision notes are prepared in a concise manner, students can use them a day before the exam to revise when time is limited.
  •         Exam stress and anxiety will therefore be greatly reduced.
  •         The revision notes are in a convenient pdf form. Students will be able to study these revision notes from anywhere and at any time using this technology.

Physical and Chemical Class 7 Science Chapter 6 – Key Takeaways

Physical Changes

During a physical change, substances go through changes only in its physical properties like size, colour, state, and shape. Most importantly, no new substance is generated in these changes. To understand the topic, it is essential to perform a few activities and see how physical changes take place around us. Generally, all the physical changes are momentary changes that can easily be reversed to create the original substance. If there is little energy as heat, it is either absorbed or evolved. For example, water can change its state from solid to liquid and liquid to gas.

Crystallisation

As seawater has salts dissolved in it, the sea becomes salty. Salt can be acquired from seawater by a procedure called evaporation. The salt acquired in this way is not pure, and its crystals are tiny. The shape of the crystals can’t be seen clearly. However, giant crystals of pure substances can be acquired from their solutions by the process of crystallisation.

The method of cooling a hot concentrated solution of a substance to acquire crystals is known as Crystallisation. It is a primary example of a physical change.

Chemical Changes

The Class 7 Science Chapter 6 Notes include chemical changes, which are also widely referred to as chemical reactions. A chemical change happens when two substances react chemically to generate a new substance with totally different chemical properties. All these new substances that we utilise in multiple fields of our life are generated due to chemical changes or chemical reactions.

Let’s take a look at an example of chemical changes. A change with which almost everyone is familiar is the rusting of iron. All the iron or steel items kept in the open space or area get rusted slowly. It develops a coating of a brownish substance known as rust, and the procedure is known as rusting. Usually, we see iron gates of farms and parks, iron benches kept in gardens, and almost all the iron items kept in the open space rusted with time. Other things, like agricultural tools, kitchen tools, etc., also get rusted. Rust is not iron; it is a different substance but gets deposited on iron.

Rusting of Iron

When an iron item is left exposed to a moist environment, it chemically reacts with oxygen and water in the air to generate a red-brown flaky substance known as rust. The following equation can represent the procedure of rusting:

Iron (Fe) + Oxygen (O₂) (From air) + Water (H₂O) Rust (Iron oxide, Fe₂O₃)

Rusting happens due to the presence of both water and oxygen. The more humid the environment, the quicker the rusting happens. The rust slowly eats away or corrodes the iron, resulting in considerable loss. As iron is utilised in building ships, cars, bridges, truck bodies, and various other items, the temporary loss because of the rusting is massive.

Also Read –


Also published on Medium.

You may also like