Comprehensive Notes on Matter in Our Surroundings

Matter in Our Surroundings

Introduction

• Everything in the universe is made up of "matter".

• Matter occupies space and has mass.

• Early Indian philosophers classified matter into five basic elements: air, earth, fire, sky, and water ("Panch Tatva").

• Modern scientists classify matter based on physical properties and chemical nature.

1.1 Physical Nature of Matter

1.1.1 Matter is Made Up of Particles

• Two schools of thought:

  • Matter is continuous (like wood).

  • Matter is particulate (like sand).

• Activity 1.1: Dissolving salt/sugar in water demonstrates that matter is made up of particles.

1.1.2 How Small Are These Particles of Matter?

• Activity 1.2: Dissolving potassium permanganate in water repeatedly shows that even after several dilutions, the color is still visible, indicating the presence of tiny particles.

• The particles of matter are very small, beyond our imagination.

1.2 Characteristics of Particles of Matter

1.2.1 Particles of Matter Have Space Between Them

• Activities 1.1 and 1.2 show that particles of sugar, salt, Dettol, or potassium permanganate get evenly distributed in water.

• When making tea, coffee, or lemonade, particles of one type of matter get into the spaces between particles of the other.

• There is enough space between particles of matter.

1.2.2 Particles of Matter Are Continuously Moving

• Activity 1.3: The smell of an unlit incense stick can only be detected up close, but when lit, the smell can be detected from a distance.

• Activity 1.4: Ink spreads evenly throughout water, while honey does so more slowly.

• Activity 1.5: A crystal of copper sulfate or potassium permanganate dissolves faster in hot water than in cold water.

• Particles of matter are continuously moving and possess kinetic energy.

• As temperature increases, particles move faster, increasing their kinetic energy.

• Particles of matter intermix on their own through diffusion.

• Diffusion becomes faster on heating.

1.2.3 Particles of Matter Attract Each Other

• Activity 1.6: Human chains are formed, and the strength required to break them varies depending on how the participants are holding each other.

• Activity 1.7: Breaking an iron nail, chalk, and rubber band requires different amounts of force, indicating varying forces of attraction between particles.

• Activity 1.8: Trying to cut the surface of water with fingers demonstrates the force that keeps water molecules together.

• Particles of matter have forces acting between them, keeping them together.

• The strength of this force of attraction varies from one kind of matter to another.

1.3 States of Matter

• Matter exists in three different states: solid, liquid, and gas.

• These states arise due to the variation in the characteristics of the particles of matter.

1.3.1 The Solid State

• Activity 1.9: Collecting articles like a pen, book, needle, and wooden stick shows they have definite shapes, distinct boundaries, and fixed volumes.

• Solids have negligible compressibility.

• Solids have a tendency to maintain their shape when subjected to outside force and are rigid.

• Exceptions:

  • A rubber band changes shape under force and regains it when the force is removed.

  • Sugar and salt crystals maintain their shape regardless of the container.

  • A sponge has minute holes filled with air, allowing compression.

1.3.2 The Liquid State

• Activity 1.10: Collecting water, cooking oil, milk, juice, and cold drink, and transferring them into different shaped containers shows that liquids have no fixed shape but have a fixed volume.

• Liquids flow and change shape, so they are not rigid but are fluid.

• Solids and liquids can diffuse into liquids.

• Gases from the atmosphere diffuse and dissolve in water, which is essential for aquatic life.

• The rate of diffusion of liquids is higher than that of solids because particles in the liquid state move freely and have greater space between them.

1.3.3 The Gaseous State

• Activity 1.11: Compressing gases in syringes demonstrates that gases are highly compressible.

• Liquefied petroleum gas (LPG) and compressed natural gas (CNG) are examples of compressed gases.

• Gases show the property of diffusing very fast into other gases due to the high speed of particles and large space between them.

• In the gaseous state, particles move about randomly at high speed.

• The pressure exerted by the gas is due to the force exerted by gas particles per unit area on the walls of the container.

1.4 Can Matter Change its State?

• Water can exist in three states: solid (ice), liquid (water), and gas (water vapor).

1.4.1 Effect of Change of Temperature

• Activity 1.12: Heating ice in a beaker demonstrates the conversion of solid to liquid and liquid to gas.

• On increasing the temperature of solids, the kinetic energy of the particles increases, causing them to vibrate with greater speed.

• The solid melts and is converted to a liquid at its melting point.

• The melting point of a solid is an indication of the strength of the force of attraction between its particles.

• The melting point of ice is $273.15 K$.

• The process of melting is also known as fusion.

• Latent heat is the heat energy absorbed without showing any rise in temperature during a change of state.

• The latent heat of fusion is the heat energy required to change $1 kg$ of a solid into liquid at atmospheric pressure at its melting point.

• Particles in water at $0^\circ C$ ($273 K$) have more energy than particles in ice at the same temperature.

• The temperature at which a liquid starts boiling at atmospheric pressure is its boiling point.

• Boiling is a bulk phenomenon.

• For water, the boiling point is $373 K$ ($100^\circ C$).

• Particles in steam at $373 K$ have more energy than water at the same temperature due to the latent heat of vaporization.

• Kelvin is the SI unit of temperature, where $0^\circ C = 273.15 K$.

• To convert Celsius to Kelvin, add 273; to convert Kelvin to Celsius, subtract 273.

1.4.2 Effect of Change of Pressure

• Applying pressure and reducing temperature can liquefy gases.

• Solid carbon dioxide ($CO_2$) is stored under high pressure and converts directly into the gaseous state on decrease of pressure to $1 atmosphere$ without becoming liquid (dry ice).

• Pressure and temperature determine the state of a substance.

• Activity 1.13: Heating camphor demonstrates sublimation.

• Sublimation is the change of state directly from solid to gas without changing into liquid.

• Deposition is the change of state directly from gas to solid without changing into liquid.

1.5 Evaporation

• Evaporation is the change of liquid into vapors at any temperature below its boiling point.

1.5.1 Factors Affecting Evaporation

• Activity 1.14: Demonstrates the effects of surface area, temperature, and wind velocity on evaporation.

• The rate of evaporation increases with:

  • An increase in surface area.

  • An increase in temperature.

  • A decrease in humidity.

  • An increase in wind speed.

1.5.2 How Does Evaporation Cause Cooling?

• The particles of liquid absorb energy from the surroundings to regain the energy lost during evaporation, making the surroundings cold.

• When acetone (nail polish remover) is poured on the palm, it evaporates, causing a cooling sensation.

• People sprinkle water on the roof or open ground after a hot sunny day because the large latent heat of vaporization of water helps to cool the hot surface.

• Cotton clothes should be worn in summer because cotton is a good absorber of water, which helps in absorbing sweat and exposing it to the atmosphere for easy evaporation.

• Water droplets appear on the outer surface of a glass containing ice-cold water because the water vapor in the air loses energy and gets converted to the liquid state.

Key Concepts

• Matter is made up of small particles with spaces between them.

• Particles are continuously moving and attract each other.

• Matter exists in three states: solid, liquid, and gas.

• States of matter are inter-convertible by changing temperature or pressure.

• Sublimation and deposition are direct conversions between solid and gas.

• Evaporation is a surface phenomenon that causes cooling.

• Boiling is a bulk phenomenon.

• Latent heat of vaporization and fusion.

Units to Remember

• Temperature: kelvin (K)

• Length: metre (m)

• Mass: kilogram (kg)

• Weight: newton (N)

• Volume: cubic metre ($m^3$)

• Density: kilogram per cubic metre ($kg/m^3$)

• Pressure: pascal (Pa)