Matter in Our Surroundings

Matter

• What is Matter?
  • Everything around us is made of matter.
  • Matter includes air, food, stones, clouds, stars, plants, animals, water, and sand.
  • Matter has mass and volume, which means it occupies space.

Ancient Understanding of Matter

• Indian View (Panch Tatva):
  • Early Indian philosophers described matter as made of five basic elements: air, earth, fire, sky, and water.
• Greek View:
  • Ancient Greek philosophers also believed that matter was made of a few fundamental elements.

Modern View of Matter

• Modern science classifies matter on the basis of:
  1. Physical properties
  2. Chemical nature

This chapter mainly deals with the physical nature and physical properties of matter.

1.1 Physical Nature of Matter

1.1.1 Matter is Made Up of Particles

Matter is particulate in nature, that is, it is made up of very small particles.

SI Units Related to Matter

• Mass: kilogram (kg).
• Volume: cubic metre (m³)

Common volume relations

• 1 litre (L) = 1 dm³
• 1 L = 1000 mL
• 1 mL = 1 cm³

1.1.2 How Small Are the Particles of Matter?

Key Points on Size of Particles

• Particles of matter are extremely small.
• They spread out and mix uniformly.
• Tiny amounts can affect large volumes of water or air.

Characteristics of Particles of Matter

1.2.1 Particles of Matter Have Space Between Them

When substances like sugar, salt, Dettol, or potassium permanganate dissolve in water, they spread uniformly.

• Explanation:
  • This happens because there is space between the particles of water.

• Daily Life Examples:
  • Tea preparation
  • Coffee preparation
  • Lemonade making

These processes show intermixing of particles due to spaces between them.

1.2.2 Particles of Matter Are Continuously Moving

Continuous Motion of Particles

• Particles of matter are always in motion and possess kinetic energy.

Activity Examples:

Effect of Temperature

• Higher temperature increases particle motion.
• Diffusion becomes faster on heating.

Key Conclusions

• Particles of matter are always moving (kinetic energy).
• They mix on their own by diffusion.
• Diffusion is faster at higher temperatures.

1.2.3 Particles of Matter Attract Each Other

Interparticle Attraction

• Particles of matter attract each other with a force.

Activity Examples:

Conclusions:

• Particles of matter have attractive forces between them.
  • This force keeps the particles together.
• Strength of attraction varies from one substance to another.

States of Matter

• Matter exists in three main states:
  1. Solid
  2. Liquid
  3. Gas

• These states differ due to differences in:
  1. Interparticle space
  2. Interparticle force
  3. Particle motion

1.3.1 The Solid State

• Properties of Solids
  • Definite shape and fixed volume.
  • Rigid and difficult to compress.
  • Strong interparticle forces.

Special Cases

• Rubber Band: Stretchable and regains shape, but breaks under excessive force.
• Sugar and Salt: Take the shape of their container but each crystal retains its shape.
  • Appear to flow but each crystal has a fixed shape.
• Sponge: Compressible due to trapped air, but still a solid.

1.3.2 The Liquid State

• Properties of Liquids:
  • No fixed shape, take the shape of their container.
  • Fixed volume.
  • Can flow, so they are fluid.

Diffusion in Liquids

• Solids and liquids diffuse in liquids.
• Gases like oxygen and carbon dioxide dissolve in water.

Importance

• Dissolved oxygen supports aquatic life.
• Diffusion is faster in liquids than in solids.

1.3.3 The Gaseous State

• Properties of Gases:
  • No fixed shape and no fixed volume.
  • Highly compressible.
  • Particles move randomly at very high speed.

• Examples of Compressed Gases
  • LPG cylinders
  • CNG in vehicles
  • Oxygen cylinders

• Behavior of Gas Particles
  • Random motion causes collisions with container walls.
  • These collisions produce gas pressure.

Smell of food diffuses quickly in air due to high speed and space between gas particles.

Summary of States of Matter

• Solids: Strong attraction, least movement, rigid.
• Liquids: Moderate attraction, moderate movement, fluid.
• Gases: Very weak attraction, maximum movement, highly compressible.

These states of matter arise due to differences in particle arrangement, motion, and forces of attraction.

Can Matter Change Its State?

• Matter can exist in different states depending on temperature and pressure.
• The same substance can change from one state to another by heating or cooling.

• Example: Water
  • Solid: Ice
  • Liquid: Water
  • Gas: Water vapour (steam)

This change in state happens due to changes in the energy and movement of particles.

1.4.1 Effect of Change of Temperature

Heating a Solid

• When a solid is heated:
  • Particles gain kinetic energy.
  • They start vibrating faster at their fixed positions.
  • At a certain temperature, particles overcome the force of attraction holding them together.

Melting

• Definition:
  • Melting is the process in which a solid changes into a liquid on heating.
• Melting Point:
  • The temperature at which a solid changes into a liquid at atmospheric pressure.
• Example:
  • Ice melts at 0°C or 273.15 K.

Latent Heat of Fusion

• Definition:
  • The amount of heat required to convert 1 kg of a solid into liquid at its melting point without any change in temperature.
• Explanation:
  • During melting, temperature remains constant.
  • Heat energy is used to overcome interparticle forces, not to raise temperature.

Freezing

• Definition:
  • Freezing is the process in which a liquid changes into a solid on cooling.
• Freezing Point:
  • The temperature at which a liquid changes into a solid.

Important Point – Melting point and freezing point of a substance are the same.

Purity and Melting Point

• A pure substance has a sharp melting point.
• Impurities lower the melting point.

Special Case: Regelation of Ice

• Ice contracts on melting.
• Its melting point decreases with increase in pressure.
• When two ice cubes are pressed together, ice melts at the contact surface and refreezes when pressure is released.
• This phenomenon is called regelation.

Heating a Liquid

• When a liquid is heated:
  • Particles move faster.
  • Interparticle attraction weakens further.
  • At a fixed temperature, particles escape into the gaseous state.

Boiling

• Definition:
  • Boiling is the process in which a liquid changes into gas throughout the bulk of the liquid.
• Boiling Point:
  • The temperature at which a liquid changes into vapour at atmospheric pressure.
• Example:
  • Water boils at 100°C or 373 K.

Latent Heat of Vaporisation

• Definition:
  • The amount of heat required to convert 1 kg of a liquid into gas at its boiling point without any change in temperature.
• Explanation:
  • At boiling point, temperature remains constant.
  • Heat energy is used to separate particles completely.

Important Point – Particles in steam have more energy than particles in water at the same temperature due to latent heat.

Vaporisation vs Boiling

• Vaporisation occurs at all temperatures.
• Boiling occurs only at a fixed temperature (boiling point).
• Rate of vaporisation is maximum at boiling point.

Effect of Cooling on Matter

Condensation

• Definition:
  • The process of changing a gas into a liquid on cooling.
  • It is the reverse of vaporisation.

Freezing During Cooling

• During freezing:
  • Temperature remains constant.
  • Heat energy is released to the surroundings.
  • A mixture of solid and liquid exists until freezing is complete.

Cooling Curve of a Substance

• Stages during cooling:
  • Liquid cools until freezing point is reached.
  • Liquid freezes at constant temperature.
  • Solid cools further after complete solidification.

Heating Curve of a Substance

• Stages during heating:
  • Solid heats up until melting point.
  • Solid melts at constant temperature.
  • Liquid heats up after complete melting.

Sublimation

• Definition:
  • Sublimation is the process in which a solid changes directly into gas without passing through the liquid state.
• Examples:
  • Camphor
  • Naphthalene
  • Ammonium chloride

Deposition (Desublimation)

• Definition:
  • The process in which a gas changes directly into a solid on cooling.
  • It is the reverse of sublimation.

Summary

• Change of state depends on temperature and pressure.
• Heating increases kinetic energy of particles.
• Melting converts solid to liquid at melting point.
• Boiling converts liquid to gas at boiling point.
• Latent heat is absorbed or released during change of state without temperature change.
• Some substances show sublimation, changing directly between solid and gas.

This explains how temperature affects particle motion and causes matter to change its state.

Effect of Change of Pressure

• States of matter differ mainly because of the distance between their particles and the strength of attraction between them.
• Along with temperature, pressure also plays an important role in changing the state of matter.

Role of Pressure in Changing State

• Interparticle Distance and Force
  • In solids, particles are very close with strong attraction.
  • In liquids, particles are slightly farther apart with moderate attraction.
  • In gases, particles are far apart with very weak attraction.

Effect of Increasing Pressure

• When pressure is applied to a gas:
  • Particles are forced closer together.
  • Interparticle space decreases.
  • Interparticle attraction increases.
• As a result:
  • Gas can change into liquid under high pressure.
  • Liquid can further change into solid under very high pressure.

Conclusion

• The physical state of a substance depends on both temperature and pressure.

Liquefaction of Gases

• Liquefaction of gases is achieved by:
  • Lowering temperature, and
  • Increasing pressure.

• Example: Solid Carbon Dioxide (Dry Ice)
  • Carbon dioxide is stored under high pressure as a solid called dry ice.
  • When pressure is reduced to 1 atmosphere, solid CO₂ changes directly into gas without becoming liquid.
  • This direct change from solid to gas is an example of sublimation.

Pressure Unit

• Atmosphere (atm):
  • A commonly used unit of pressure.

• 1 atm = 1.01 × 10⁵ pascal (Pa).
• Normal atmospheric pressure at sea level is 1 atm.

Key Point

• Both temperature and pressure together determine whether a substance exists as a solid, liquid, or gas.

Evaporation

• Everyday Examples of Evaporation:
  • Water left in an open vessel slowly disappears.
  • Wet clothes dry on a clothesline.

• Definition of Evaporation
  • Evaporation is the process by which a liquid changes into vapour at any temperature below its boiling point.

Why Evaporation Occurs

• Continuous Motion of Particles
  • Particles of matter are always in motion.
  • Some particles at the surface of a liquid have higher kinetic energy.
• Surface Phenomenon
  • High-energy surface particles overcome the force of attraction.
  • They escape into the air as vapour.

Evaporation is an endothermic process because energy is absorbed from surroundings.

Factors Affecting Evaporation

Factors

1. Surface Area
   • Larger surface area increases evaporation rate.
   • Example: Spreading clothes helps them dry faster.
2. Temperature
   • Higher temperature increases kinetic energy of particles.
   • This speeds up evaporation.
3. Humidity
   • Humidity refers to the amount of water vapour present in air.
   • Lower humidity allows faster evaporation.
   • High humidity slows down evaporation.
4. Wind Speed
   • Higher wind speed removes vapour particles from the surface.
   • This increases the rate of evaporation.

How Evaporation Causes Cooling

1. Energy Absorption
   • High-energy particles escape during evaporation.
   • Remaining particles lose average kinetic energy.
2. Cooling Effect
   • To regain energy, the liquid absorbs heat from surroundings.
   • This lowers the temperature of the surroundings.

Daily Life Examples of Cooling by Evaporation

1. Acetone on Palm
   • Acetone evaporates quickly.
   • It absorbs heat from skin, giving a cooling sensation.
2. Sprinkling Water on Floors
   • Water evaporates using heat from the surface.
   • This cools the floor and nearby air.
3. Cotton Clothes in Summer
   • Cotton absorbs sweat easily.
   • Sweat evaporates, removing heat from the body.

Condensation (Related Concept)

• Condensation
  • Condensation is the change of gas into liquid on cooling.
• Example
  • Water droplets form on the outside of a cold glass.
  • Water vapour in air loses energy and condenses into liquid droplets.

Summary

• Pressure and temperature together control the state of matter.
• Increasing pressure brings particles closer and can change gas to liquid or solid.
• Evaporation occurs at all temperatures below boiling point.
• Evaporation depends on surface area, temperature, humidity, and wind speed.
• Evaporation causes cooling by absorbing heat from surroundings.

Chapter Summary

• Nature of Matter
  • Matter is made up of very small particles.
  • Everything around us exists as matter and shows physical diversity.
• States of Matter
  • Matter exists in three states: solid, liquid, and gas.

Interparticle Forces

• The force of attraction between particles is:
  • Maximum in solids.
  • Intermediate in liquids.
  • Minimum in gases.

Interparticle Space and Kinetic Energy

• Spaces between particles are:
  • Minimum in solids.
  • Intermediate in liquids.
  • Maximum in gases.

• Kinetic energy of particles is:
  • Least in solids.
  • Moderate in liquids.
  • Maximum in gases.

Arrangement of Particles

• In solids, particles are closely packed and highly ordered.
• In liquids, particles can slip and slide past each other.
• In gases, particles move randomly in all directions.

Change of State of Matter

• States of matter are inter-convertible.
• Change of state can be brought about by changing temperature or pressure.

Special Changes of State

• Sublimation: Direct change of solid to gas without becoming liquid.
• Deposition: Direct change of gas to solid without becoming liquid.

Boiling and Evaporation

• Boiling is a bulk phenomenon where particles from the entire liquid change into vapour.
• Evaporation is a surface phenomenon where only surface particles gain energy and change into vapour.

Factors Affecting Evaporation

• Rate of evaporation depends on:
  • Surface area.
  • Temperature.
  • Humidity.
  • Wind speed.

Cooling Effect of Evaporation

• Evaporation causes cooling because particles absorb energy from the surroundings.

Latent Heat

• Latent Heat of Fusion:
  • Heat energy required to change 1 kg of solid into liquid at its melting point.

• Latent Heat of Vaporisation:
  • Heat energy required to change 1 kg of liquid into gas at its boiling point.

Measurable Quantities and Units

1. Temperature
   • Unit: kelvin (K)
2. Length
   • Unit: metre (m)
3. Mass
   • Unit: kilogram (kg)
4. Weight
   • Unit: newton (N)
5. Volume
   • Unit: cubic metre (m³)
6. Density
   • Unit: kilogram per cubic metre (kg/m³)
7. Pressure
   • Unit: pascal (Pa)