Learning Objectives
- Understand the physical nature of matter
- Learn the characteristics of particles of matter
- Classify matter into solid, liquid, and gas based on properties
- Understand the effect of change of temperature and pressure on states of matter
- Learn about evaporation and the factors affecting it
Key Concepts
Physical Nature of Matter
Matter is made up of tiny particles. These particles are very small and cannot be seen with the naked eye. Evidence: dissolving sugar in water — it disappears but makes the water sweet, proving particles exist and mix.
Characteristics of Particles of Matter
- Particles have spaces between them: When sugar dissolves in water, it occupies the spaces between water particles.
- Particles are continuously moving: They possess kinetic energy. This movement increases with temperature. Diffusion occurs because of this motion.
- Particles attract each other: There is a force of attraction between particles that holds them together.
States of Matter
Solid: Fixed shape and volume. Particles are closely packed with strong intermolecular forces. Incompressible. Very low kinetic energy. Examples: ice, wood, iron.
Liquid: Fixed volume but no fixed shape (takes the shape of the container). Moderate intermolecular forces. Flows. Examples: water, milk, oil.
Gas: Neither fixed shape nor fixed volume. Particles are far apart with weak intermolecular forces. Highly compressible. High kinetic energy. Examples: air, oxygen, carbon dioxide.
Change of State
Melting (Fusion): Solid → Liquid. Temperature at which solid melts = melting point. Melting point of ice = 0°C (273.16 K).
Boiling (Vaporisation): Liquid → Gas. Temperature at which liquid boils = boiling point. Boiling point of water = 100°C (373.16 K).
Condensation: Gas → Liquid.
Freezing: Liquid → Solid.
Sublimation: Solid → Gas directly (without passing through liquid state). Examples: camphor, naphthalene balls, dry ice.
Deposition: Gas → Solid directly.
Latent heat: The heat energy absorbed or released during change of state without any change in temperature.
Latent heat of fusion: 334 J/g for ice. Latent heat of vaporisation: 2260 J/g for water.
Effect of Pressure
Increasing pressure and reducing temperature can liquefy gases. Example: LPG (Liquefied Petroleum Gas) is stored under high pressure as liquid.
Evaporation
Evaporation is the process of a liquid changing to vapour at any temperature below its boiling point. It occurs at the surface.
Factors affecting evaporation: Surface area (more area = faster), temperature (higher = faster), humidity (lower humidity = faster), wind speed (more wind = faster).
Evaporation causes cooling: Particles with higher energy escape, lowering the average energy and temperature. Example: sweating cools our body.
Summary
Matter is made of particles with spaces between them. These particles move continuously and attract each other. Matter exists in three states — solid, liquid, and gas — determined by the intermolecular forces and kinetic energy of particles. Changes of state occur by changing temperature or pressure. Evaporation is a surface phenomenon that causes cooling.
Important Terms
- Diffusion: Intermixing of particles of two different substances on their own
- Latent Heat: Heat absorbed during change of state without temperature change
- Sublimation: Direct conversion of solid to gas without becoming liquid
- Evaporation: Conversion of liquid to vapour at any temperature below boiling point
- Boiling Point: Temperature at which a liquid starts boiling
- Melting Point: Temperature at which a solid starts melting
Quick Revision
- Matter is made of tiny, constantly moving particles with spaces between them
- Solid → Liquid (melting), Liquid → Gas (boiling), Solid → Gas (sublimation)
- Melting point of ice = 0°C; Boiling point of water = 100°C
- Latent heat is absorbed/released during change of state at constant temperature
- Evaporation causes cooling; increases with temperature, surface area, and wind speed