Matter in Our Surroundings Class 9 Science Chapter 1 Notes

Matter in Our Surroundings Class 9 Science Notes: These notes provide a clear summary and quick revision guide for Class 9 Science Chapter 1 – Matter in Our Surroundings. They include important key points, diagrams, and concise explanations designed to help students review the entire chapter efficiently.

Chapter 1 of the Class 9 Science NCERT textbook introduces students to the concept of matter, its physical states, and how changes in temperature and pressure affect these states. It explains properties like diffusion, evaporation, condensation, and melting with the help of practical examples and illustrations.

If you are studying from the NCERT Science book, these revision notes will make it easier to remember essential concepts. You’ll find short key points, neatly organized summaries, and diagrams that simplify understanding.

After going through these CBSE Class 9 notes, also refer to the NCERT Solutions for Class 9 Science Chapter 1 for detailed answers and problem-solving practice. Together, they make a complete study resource for mastering Matter in Our Surroundings.

CBSE Class 9 Science Notes Chapter 1 Matter In Our Surroundings

Introduction to Matter

• Matter is anything that has mass and occupies space.
• Everything around us - air, water, rocks, metals, and even living beings is made of matter.
• The smallest unit of matter is a particle, and these particles are too tiny to be seen with the naked eye.

States of Matter

Matter is divided into solids, liquids, and gases based on how their particles are arranged and the strength of attraction between them. These states can change from one form to another by altering temperature or pressure. For instance, when the temperature rises, ice (solid) melts and becomes water (liquid).

Physical Nature of Matter

A physical property is a characteristic of matter that can be observed or measured without altering its chemical composition. These properties do not depend on the quantity of matter. Common physical properties include appearance, color, odor, density, texture, melting point, boiling point, and solubility.

Characteristics of Particles of Matter

1. Matter is made up of particles. Example: When sugar dissolves in water, its particles spread throughout — though invisible, they are still present.
2. Particles of matter are very small.
3. Particles of matter have spaces between them.
4. Particles of matter move continuously. Heating increases their movement (kinetic energy).
5. Particles of matter attract each other. The strength of attraction varies among solids, liquids, and gases.

Diffusion

Diffusion is the process in which particles of one substance mix freely with those of another on their own, such as ink spreading in water. During this process, the particles move into the spaces between other particles. The rate of diffusion increases with a rise in temperature, because higher temperature gives particles more kinetic energy, making them move faster.

Effect of Change of Temperature on the State of Matter

When the temperature increases, the kinetic energy of the particles also rises, causing them to vibrate faster and with greater energy. This weakens the interparticle forces of attraction, allowing the particles to move more freely.

As a result, the state of matter changes - solids melt to become liquids, and liquids further change into gases when heated.

Melting Point

The melting point of a solid is the temperature at which it changes into a liquid under normal atmospheric pressure. At this temperature, the solid and liquid phases coexist in equilibrium, meaning both states exist together until the solid completely melts.

Fusion

Fusion is the process in which two lighter atoms combine to form a heavier one, for example, when two hydrogen atoms fuse to produce a helium atom. This reaction releases an enormous amount of energy, far greater than that produced by fission, and it is the source of the Sun’s energy. Unlike fission, fusion does not create radioactive byproducts. The melting point of ice, the temperature at which solid ice changes into liquid water is 0°C (32°F).

Boiling Point

The boiling point of a liquid is the temperature at which its vapour pressure becomes equal to the surrounding atmospheric pressure. At this temperature, the liquid starts changing into its gaseous state. For example, water boils at 100°C under normal atmospheric conditions. Interestingly, the Celsius temperature scale was originally defined using two key reference points — the melting point of ice (0°C) and the boiling point of water (100°C).

Latent Heat of Fusion

It is the quantity of heat energy needed to convert 1 kilogram of a solid into a liquid at its melting point under atmospheric pressure.

Latent Heat of Vaporisation

It is the quantity of heat energy needed to convert 1 kilogram of a solid into a liquid at its melting point under atmospheric pressure.

Sublimation

Sublimation is the process in which a substance changes directly from the solid state to the gaseous state or from gas to solid without passing through the liquid state.

Effect of Pressure and Temperature on State

• Increasing temperature: Changes solids to liquids and liquids to gases.
• Increasing pressure: Can convert gases into liquids.
• Example: LPG and CNG are stored under high pressure in liquid form.

Flowchart for Inter-Conversion of the Three States of Matter

Evaporation

Evaporation is the process in which molecules in a liquid spontaneously change into the gaseous state at temperatures below the liquid’s boiling point. For example, damp clothes dry gradually because water in them evaporates into water vapour.

Factors Affecting Evaporation

• Temperature: Higher temperature increases the rate of evaporation.
• Surface Area: A larger surface area allows faster evaporation.
• Humidity: Greater humidity reduces the rate of evaporation.
• Wind Speed: Stronger wind enhances the rate of evaporation.

Applications of Evaporative Cooling

• Water is kept cool in earthen pots because their porous surface allows more evaporation, similar to the pores in cotton fabric.
• Our bodies also stay cool through sweating. When sweat evaporates, it absorbs heat from the body, reducing body temperature.
• In summer, we wear cotton clothes because cotton absorbs sweat effectively and exposes it to air, increasing evaporation and giving a cooling effect.

Important Study Materials for Class 9 - Science