CBSE Class 9 Science Notes Chapter 1 Matter in Our Surroundings

Matter is anything that occupies space and has mass. It forms everything around us. These Matter In Our Surroundings Class 9 Notes explains the fundamental nature of matter, its particle characteristics, and the different states it can exist in. Understanding matter is important for building a strong foundation in science.

Matter In Our Surroundings Class 9 Notes

Matter consists of tiny particles. These particles are incredibly small, far too small to see with the naked eye. Even a small drop of water contains millions of these particles. 

Characteristics of Matter Particles

Particles of matter show specific behaviors. These traits define how matter interacts and changes.

Space Between Particles: There is empty space between the particles of matter. This allows substances to mix or dissolve. For example, when sugar dissolves in water, sugar particles fit into spaces between water particles.

• Solids: Have the least space.

• Liquids: Have more space than solids.

• Gases: Have the largest space.

Continuous Particle Motion: Particles of matter are always moving. They possess kinetic energy, which increases with temperature. This continuous motion leads to diffusion. Diffusion is the intermixing of substances due to particle movement.

• Solids: Particles vibrate at fixed positions.

• Liquids: Particles can slide over each other.

• Gases: Particles move freely and rapidly.

Particle Attraction: Particles of matter attract each other. This force of attraction varies between different states. This force keeps particles together.

• Solids: Strongest force of attraction.

• Liquids: Moderate force of attraction.

• Gases: Weakest force of attraction.

Chapter 1 Matter In Our Surroundings Class 9 Notes​ States of Matter

Matter primarily exists in three states: solid, liquid, and gas. Each state has unique properties due to the arrangement and interaction of its particles. Below are the properties of states of matter: 

Change of State of Matter

Matter can change from one state to another by altering temperature or pressure.

• Effect of Temperature:

• Melting (Fusion): Solid changes to liquid upon heating. The melting point is the temperature at which this occurs. Ice melts at 0°C or 273 K.

• Boiling (Vaporization): Liquid changes to gas upon heating. The boiling point is the temperature at which this occurs. Water boils at 100°C or 373 K.

• Condensation: It is the process in which gas changes to liquid upon cooling.

• Freezing (Solidification): It is the process in which the liquid changes to solid upon cooling.

• Latent Heat: This is the hidden heat energy absorbed or released during a change of state without a temperature change.

• Latent Heat of Fusion: It is the amount of heat required to change 1 kg of solid to liquid at its melting point. 

• Latent Heat of Vaporization: It is the amount of heat required to change 1 kg of liquid to gas at its boiling point. 

Sublimation and Deposition:

• Sublimation is the process in which a solid substance directly changes into its gaseous state without passing through the liquid state. This happens because the particles of some solids have enough energy to overcome the force of attraction between them and escape directly into the air on heating. Common substances that undergo sublimation include camphor, naphthalene, ammonium chloride, and dry ice.

• Deposition: It is also known as desublimation. It is a phase transition where a substance changes directly from a gas to a solid without ever becoming a liquid.

• Effect of Pressure: Pressure primarily affects gases. Increasing pressure and reducing temperature can convert gases into liquids. Examples include LPG and CNG.

Evaporation

Evaporation is the process where liquid particles at the surface escape into vapor. This process occurs at any temperature below the boiling point and only at the surface. Evaporation causes cooling. Particles absorb heat from surroundings to change state, making the surroundings cooler.

• Factors Affecting Evaporation:

• Surface Area: Larger surface area increases the evaporation rate.

• Temperature: Higher temperature increases evaporation rate.

• Humidity: Lower humidity increases evaporation rate.

• Wind Speed: Higher wind speed increases evaporation rate.

Diffusion

Diffusion is the process of mixing and spreading out of a substance into another substance due to the movement or motion of its particles. This phenomenon occurs until a homogeneous mixture is achieved, where the substances are evenly distributed.

For example , if you place a crystal of potassium permanganate (which is purple in color) into a beaker filled with water, you'll observe that the purple color begins to spread throughout the water. This happens because the particles of potassium permanganate are in constant motion and move randomly in all directions.

Over time, the purple color will continue to spread until the entire solution turns purple, indicating that diffusion has occurred. This process demonstrates how substances can mix and spread out to create a uniform concentration throughout a solution.

Key Mechanisms of Matter In Our Surroundings

Temperature Conversion Rules

Temperature is a key factor in state changes. Kelvin (K) is the SI unit, while Celsius (°C) is another common unit.

• Celsius to Kelvin:
  K = °C + 273

• Kelvin to Celsius:
  °C = K - 273

Latent Heat Principles

When matter changes state (melting, boiling, freezing), heat energy is absorbed or released, but the temperature doesn’t change during the transition. This heat is called latent heat.

• Why temperature stays constant: The energy is used to break or form intermolecular forces, not to increase kinetic energy.

• Examples:

• Melting ice: Heat energy is absorbed to break bonds between water molecules → ice becomes water, temperature stays 0°C.
  
  

• Boiling water: Heat energy is used to separate water molecules → water becomes steam, temperature stays 100°C.