CBSE Class 9 Science Notes Chapter 1 Matter In Our Surroundings
States of Matter
- Matter can be classified as solid, liquid or gas on the basis of interparticle forces and the arrangement of particles.
- These three forms of matter are interconvertible by increasing or decreasing pressure and temperature. For example, ice can be converted from solid to a liquid by increasing the temperature.
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| Property | Solid | Liquid | Gas |
| Shape and volume | Fixed shape and volume | No fixed shape but has volume | Neither definite shape nor volume |
| Energy | Lowest | Medium | Highest |
| Compressibility | Difficult | Nearly difficult | Easy |
| Arrangement of molecules | Regular and closely arranged | Random and little sparsely arranged | Random and more sparsely arranged |
| Fluidity | Cannot flow | Flows from higher to lower level | Flows in all directions |
| Movement | Negligible | Depends on interparticle attraction | Free, constant and random |
| Interparticle space | Very less | More | Large |
| Interparticle attraction | Maximum | Medium | Minimum |
| Density | Maximum | Medium | Minimum |
| Rate of diffusion | Negligible | It depends on interparticle attraction. | Maximum |
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Atomic View of the Three States of Matter
Physical Nature of Matter
- A physical property is an aspect of matter that can be observed or measured without changing its nature or composition.
- It is independent of the amount of matter present.
- Physical properties include appearance, colour, odour, density, texture, melting point, boiling point, solubility, etc.
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Characteristics of Particles of Matter
Matter
Matter is anything that has mass and occupies space.
- Everything that we can touch, see, hear, taste and also smell is matter.
- It is made up of really tiny particles which cannot be seen through the eye.
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The particles of which the matter is comprised influence its state and properties (physical and chemical).
1. Particles of matter have spaces between them
- This characteristic is one of the concepts behind the solubility of a substance in other substances. For example, on dissolving sugar in water, there is no rise in the water level because the particles of sugar get into the interparticle spaces between the water particles.
2. Particles of matter are always in motion
- Particles of matter show continuous random movements due to the kinetic energy they possess.
- A rise in temperature increases the kinetic energy of the particles, making them move more vigorously.
3. Particles of matter attract each other
In every substance, there is an interparticle force of attraction acting between the particles. To break a substance, we need to overcome this force. The strength of the force differs from one substance to another.
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Diffusion
When the particles of matter intermix on their own with each other, the phenomenon is called diffusion. For example, spreading of ink in water.
- During diffusion, the particles occupy the interparticle spaces.
- The rate of diffusion increases with an increase in temperature due to increase in the kinetic energy of the particles.
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Can Matter Change Its State?
Effect of Change of Temperature on the State of Matter
On increasing the temperature, the kinetic energy of the particles of the matter increases, and they begin to vibrate with higher energy. Therefore, the interparticle force of attraction between the particles reduces, and particles get detached from their position and begin to move freely.
- As a result, the state of matter begins to change.
- Solids undergo a phase change to form liquids.
- Similarly, liquids also undergo a phase change to form gases.
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Melting Point
The melting point of a solid is defined as the temperature at which solid melts to become liquid at the atmospheric pressure.
- At the melting point, these two phases, i.e., solid and liquid, are in equilibrium, i.e., at this point, both solid state and liquid state exist simultaneously.
Fusion
When two atoms collide to create a heavier atom, such as when two hydrogen atoms combine to create one helium atom, this process is known as fusion. This process generates enormous amounts of energy, many times more than fission, and powers the sun. Furthermore, it doesn’t generate radioactive fission products.
The melting point at which ice, a solid, turns to water, a liquid, is 32°F (0°C).
Boiling Point
The boiling point of a liquid is defined as the temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure.
The boiling point for any material is the temperature point at which the material transforms into the gas phase in the liquid phase. This happens at 100 degrees centigrade for water. The Celsius scale was in fact created on the basis of the ice/water melting point and the liquid water/vapor boiling point.
Read more: Celsius to Kelvin
Latent Heat of Fusion
It is the amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point.
Latent Heat of Vaporisation
It is the amount of heat energy that is required to change 1 kg of a liquid into gas at atmospheric pressure at its boiling point.
Sublimation
The transition of a substance directly from its solid phase to gaseous phase without changing into the liquid phase (or vice versa) is called sublimation.
Effect of Change in Pressure on the State of Matter
By applying pressure, the interparticle spaces between particles of matter decrease. Thus, by applying pressure and reducing temperature, we can convert a solid to liquid and a liquid to gas.
Flowchart for Inter-Conversion of the Three States of Matter
Evaporation
The phenomenon by which molecules in liquid state undergo a spontaneous transition to the gaseous phase at any temperature below its boiling point is called evaporation.
- For example, the gradual drying of damp clothes is caused by the evaporation of water to water vapour.
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Factors Affecting Evaporation
- Temperature: The rate of evaporation increases with an increase in temperature.
- Surface area: The rate of evaporation increases with an increase in surface area.
- Humidity: The rate of evaporation decreases with an increase in humidity.
- Wind speed: The rate of evaporation increases with an increase in wind speed.
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Cooling Due to Evaporation
During evaporation, the particles of a liquid absorb energy from the surroundings to overcome the inter-particle forces of attraction and undergo phase change. The absorption of heat from the surrounding makes the surroundings cool.
For example, sweating cools down our body.
Applications of Evaporative Cooling
- To keep water cool, it is kept in earthenware containers. Similar to the pores in cotton fabric, the pores in the earthen pot’s surface area allow for more evaporation.
- To keep our bodies cool, we sweat a lot. Evaporation is what transpiration ultimately is. Our body’s water evaporates, using energy in the process and lowering our body temperature as a result.
- We dress in cotton during the summer. Since cotton is a powerful water absorbent, it allows more perspiration to come into touch with the air, promoting more evaporation. We have a cooling effect when wearing cotton clothing because of this.
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Frequently Asked Questions on CBSE Class 9 Biology Notes Chapter 1 Matter in Our Surroundings
What is the ‘latent heat of fusion’?
The latent heat of fusion is the enthalpy change of any amount of substance when it melts.
What does ‘sublimation critical point’ mean?
The sublimation critical point refers to the maximum or minimum temperature and pressure beyond which the state of the matter cannot be changed.
What does ‘interconversion of matter’ mean?
Interconversion of matter refers to the change from one state to another. It is a process by which matter changes from one state to another and back to its original state without any change in its chemical composition.
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