Matter In Our Surroundings | Class 9
- Matter refers to anything that has mass and occupies space. It includes substances like hydrogen, oxygen, sugar, sand, air, and water, which are made up of tiny particles with space between them.
- Matter can exist in three states: solid, liquid, and gas. The classification is based on interparticle forces and particle arrangement. Solids have a fixed shape and volume, liquids have no fixed shape but have volume, and gases have neither definite shape nor volume.
- The states of matter are interconvertible by changing pressure and temperature. For example, ice (solid) can be converted into water (liquid) by increasing the temperature.
Table: Properties of Solid, Liquid, and Gas
|Shape and volume
|Fixed shape and volume
|No fixed shape but has volume
|Neither definite shape nor volume
|Arrangement of molecules
|Regular and closely arranged
|Random and little sparsely arranged
|Random and more sparsely arranged
|Flows from higher to lower level
|Flows in all directions
|Depends on interparticle attraction
|Free, constant, and random
|Rate of diffusion
|It depends on interparticle attraction.
Physical Nature of Matter
- Physical properties of matter are observable or measurable characteristics that do not change the nature or composition of the substance.
- These properties are independent of the amount of matter present and include appearance, color, odor, density, texture, melting point, boiling point, solubility, etc.
Characteristics of Particles of Matter
- Particles of matter have spaces between them:
- The solubility of a substance in other substances is related to this characteristic.
- When sugar dissolves in water, the sugar particles fill the interparticle spaces between the water particles without increasing the water level.
- Particles of matter are always in motion:
- The kinetic energy possessed by particles of matter causes them to exhibit continuous random movements.
- Increasing the temperature increases the kinetic energy, making the particles move more vigorously.
- Particles of matter attract each other:
- Every substance has interparticle forces of attraction between its particles.
- Breaking a substance requires overcoming this force, which varies in strength between different substances.
- Diffusion is the phenomenon of particles intermixing with each other spontaneously.
- During diffusion, particles occupy interparticle spaces and move from higher to lower concentration areas.
- The rate of diffusion increases with higher temperature due to increased particle kinetic energy.
Can Matter Change Its State?
- Changing the temperature of matter affects the kinetic energy of its particles.
- Increasing temperature increases the kinetic energy, weakening the interparticle forces and allowing particles to move freely.
- Solids can change to liquids, and liquids can change to gases when their respective interparticle forces are weakened.
- The melting point is the temperature at which a solid changes to a liquid at atmospheric pressure.
- At the melting point, both solid and liquid states coexist in equilibrium.
- The boiling point is the temperature at which the vapor pressure of a liquid equals the atmospheric pressure.
- It represents the temperature at which a substance changes from the liquid phase to the gas phase.
Latent Heat of Fusion
- The latent heat of fusion is the amount of heat energy required to convert 1 kg of a solid into a liquid at its melting point and atmospheric pressure.
Latent Heat of Vaporisation
- The latent heat of vaporization is the amount of heat energy required to convert 1 kg of a liquid into a gas at its boiling point and atmospheric pressure.
- Sublimation is the phase transition in which a substance directly changes from the solid phase to the gaseous phase (or vice versa) without passing through the liquid phase.
Effect of Change in Pressure on the State of Matter
- By applying pressure and reducing temperature, the interparticle spaces between particles of matter decrease.
- This allows for the conversion of a solid to a liquid and a liquid to a gas.
- Evaporation is the process by which molecules in the liquid state transition to the gaseous phase below the boiling point.
- Factors affecting evaporation include temperature, surface area, humidity, and wind speed.
Cooling Due to Evaporation
- During evaporation, particles of a liquid absorb energy from the surroundings to overcome interparticle forces and change phase.
- The absorption of heat causes a cooling effect in the surroundings.
- For example, sweating cools down our bodies.
Applications of Evaporative Cooling
- Earthenware containers are used to keep water cool. The porous surface of the pot allows for increased evaporation, thus cooling the water inside.
- Evaporation of sweat from our bodies helps cool us down.
Wearing cotton clothing in the summer promotes evaporation, resulting in a cooling effect.
Read More: THE FUNDAMENTAL UNIT OF LIFE- CELL| Class 9
Question and Answers
(a) 293 K = 20°C
(b) 470 K = 197°C
(a) 25°C = 298 K
(b) 373°C = 646 K
Give reason for the following observations. (a) Naphthalene balls disappear with time without leaving any solid.
Naphthalene balls disappear without leaving any solid because of sublimation. Naphthalene undergoes direct sublimation, where it changes from a solid to a gas without passing through the liquid state.
Give reason for the following observations. (b) We can get the smell of perfume sitting several metres away.
We can smell perfume sitting several meters away because perfume molecules are volatile. Volatile substances have high vapor pressure, allowing their molecules to evaporate easily and travel through the air, reaching our noses even from a distance
Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen.
Arrangement in increasing order of forces of attraction: Oxygen < Sugar < Water
In this case, the substances are arranged in increasing order of interparticle forces of attraction. Oxygen has relatively weak interparticle forces, sugar has moderate forces, and water has stronger forces due to hydrogen bonding.
Physical state of water:
(a) At 25°C, water is in the liquid state.
(b) At 0°C, water is in the solid state (ice).
(c) At 100°C, water is in the gaseous state (steam).
Reasons for physical states: (a) Water at room temperature is a liquid because the interparticle forces of attraction between water molecules are moderate. These forces allow the molecules to move freely but still remain close to each other.
An iron almirah is a solid at room temperature because the interparticle forces of attraction in solids are strong. In metals like iron, the metallic bonding between atoms creates a rigid structure, resulting in a solid state at normal room temperature.
Ice at 273 K (0°C) is more effective in cooling than water at the same temperature because ice requires energy (heat) to melt and convert into water. This energy is taken from the surroundings, resulting in a cooling effect. Once all the ice has melted, the temperature of the water can start to rise.
Steam produces more severe burns compared to boiling water because steam carries a larger amount of latent heat. Steam has absorbed additional heat energy to change its state from liquid to gas, and when it comes in contact with the skin, it releases this latent heat rapidly, causing more severe burns than boiling water.
The 'latent heat of fusion' is the amount of heat energy required to convert a substance from its solid state to its liquid state at a constant temperature and pressure. It is the energy absorbed or released during the phase change of a substance without a change in temperature.
The 'sublimation critical point' refers to the specific temperature and pressure at which a substance undergoes sublimation, transitioning directly from the solid phase to the gas phase without passing through the liquid phase. It is the point at which the substance's vapor pressure is equal to the external pressure, allowing sublimation to occur.
Which of the following are matter? Chair, air, love, smell, hate, almonds, thought, cold, lemon water, the smell of perfume.
The following substances are matter: