Comprehensive Notes on Matter in Our Surroundings

Matter in Our Surroundings

Introduction

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

• Matter occupies space and has mass (mass and volume).

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

• Ancient Greek philosophers had a similar classification.

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

• This chapter focuses on the physical properties of matter, with chemical aspects discussed later.

1.1 Physical Nature of Matter

1.1.1 Matter is Made Up of Particles

• Two schools of thought exist:

  • Matter is continuous (like wood).

  • Matter is particulate (like sand).

• Activity 1.1 demonstrates that matter is made of particles.

  • Dissolving salt or sugar in water shows the substance spreads throughout the water.

1.1.2 How Small Are These Particles of Matter?

• Activity 1.2 demonstrates the small size of particles.

  • Diluting potassium permanganate solution repeatedly still results in a colored solution.

  • This indicates that one crystal contains millions of tiny particles dividing into smaller particles.

  • The same activity can be done using 2 mL of Dettol instead of potassium permanganate.

• Particles of matter are very small, beyond imagination.

1.2 Characteristics of Particles of Matter

1.2.1Particles of Matter Have Space Between Them

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

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

• This indicates enough space exists between particles of matter.

1.2.2 Particles of Matter Are Continuously Moving

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

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

• Particles of matter intermix on their own (diffusion) by getting into the spaces between particles.

• Diffusion becomes faster on heating.

• Activities 1.3, 1.4, and 1.5 demonstrate continuous movement.

  • Activity 1.3: Smell of incense stick travels.

  • Activity 1.4: Ink and honey diffuse in water at different rates.

  • Activity 1.5: Copper sulphate or potassium permanganate dissolves faster in hot water.

1.2.3 Particles of Matter Attract Each Other

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

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

• Activity 1.6, 1.7, and 1.8 demonstrate the force of attraction.

  • Activity 1.6: Human chains are broken with varying ease depending on how they are formed.

  • Activity 1.7: Breaking iron nail, chalk, and rubber band requires different amounts of force.

  • Activity 1.8: Trying to cut the surface of water with fingers fails because water molecules are held together.

1.3 States of Matter

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

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

1.3.1 The Solid State

• Activity 1.9: Collect items like a pen, book, needle, and wooden stick to examine their properties.

• Solids have a definite shape, distinct boundaries, and a fixed volume (negligible compressibility).

• Solids tend to maintain their shape when subjected to outside force.

• Solids may break under force but are rigid and difficult to change shape.

• Examples:

  • Rubber band: Changes shape under force but regains it when the force is removed (unless excessive force is applied).

  • Sugar and salt: Each crystal's shape remains fixed regardless of the container.

  • Sponge: Has minute holes filled with air; compressing it expels the air.

1.3.2 The Liquid State

• Activity 1.10: Use liquids like water, cooking oil, milk, juice, and cold drink to observe their properties.

• Liquids have no fixed shape but have a fixed volume.

• They take up the shape of the container in which they are kept.

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

• Solids, liquids, and gases can diffuse into liquids.

• Gases from the atmosphere diffuse and dissolve in water, which is essential for aquatic life (e.g., oxygen and carbon dioxide).

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

1.3.3 The Gaseous State

• Gases are highly compressible compared to solids and liquids.

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

• Activity 1.11 demonstrates the compressibility of gases using syringes.

• Gases diffuse very fast into other gases due to the high speed of particles and large spaces between them.

• Particles in the gaseous state move randomly at high speed, hitting each other and the walls of the container.

• 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 to observe the change of state.

• Increasing the temperature of solids increases the kinetic energy of the particles, causing them to vibrate faster.

• The energy supplied by heat overcomes the forces of attraction between the particles.

• The solid melts and is converted to a liquid.

• The melting point is the minimum temperature at which a solid melts to become a liquid at atmospheric pressure.

• The melting point indicates the strength of the force of attraction between its particles.

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

• Melting (change of solid state into liquid state) is also known as fusion.

• During melting, the temperature remains the same as the heat energy is used to overcome the forces of attraction between the particles (latent heat).

• The latent heat of fusion is the amount of heat energy required to change 1 kg of a solid into a 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.

• At the boiling point, a liquid starts changing into a gas.

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

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

• Latent heat of vaporization is the extra energy absorbed by particles in steam at $373 K$ ($100^\circ C$) compared to water at the same temperature.

Note: Kelvin is the SI unit of temperature, $0^\circ C = 273.15 K$. For convenience, we take $0^\circ C = 273 K$ after rounding off the decimal. To change a temperature on the Kelvin scale to the Celsius scale you have to subtract 273 from the given temperature, and to convert a temperature on the Celsius scale to the Kelvin scale you have to add 273 to the given temperature.
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• Substances can change directly from solid to gaseous state and vice versa without changing into the liquid state.

• Activity 1.13 demonstrates sublimation using camphor.

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

1.4.2 Effect of Change of Pressure

• The difference in various states of matter is due to the difference in the distances between the constituent particles.

• Applying pressure and reducing temperature can liquefy gases.

• Solid carbon dioxide ($CO_2$) (dry ice) gets converted directly into the gaseous state on decrease of pressure to 1 atmosphere without coming into the liquid state.

• Pressure and temperature determine the state of a substance.

• 1 atmosphere = $1.01 \times 10^5 Pa$. The pressure of air in the atmosphere is called atmospheric pressure.

1.5 Evaporation

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

1.5.1 Factors Affecting Evaporation

• Evaporation is a surface phenomenon.

• The rate of evaporation increases with:

  • Increase of surface area.

  • Increase of temperature.

  • Decrease in humidity.

  • Increase in wind speed.

• These factors are demonstrated in Activity 1.14, where water is placed in different conditions to observe evaporation rates.

1.5.2 How Does Evaporation Cause Cooling?

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

• Examples:

  • Acetone (nail polish remover) on the palm.

  • Sprinkling water on a roof after a hot day.

  • Wearing cotton clothes in summer (cotton absorbs sweat and exposes it for evaporation).

• Water droplets on the outer surface of a glass containing ice-cold water are formed when water vapor loses energy and gets converted to the liquid state.

Key Concepts

• Matter is made up of small particles.

• The three states of matter are solid, liquid, and gas.

• Forces of attraction are maximum in solids, intermediate in liquids, and minimum in gases.

• Spaces between particles and kinetic energy are minimum in solids, intermediate in liquids, and maximum in gases.

• Arrangement of particles is most ordered in solids, layers of particles can slip in liquids, and there is no order in gases.

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

• Sublimation: Solid to gas directly.

• Deposition: Gas to solid directly.

• Boiling: A bulk phenomenon where particles throughout the liquid change into the vapor state.

• Evaporation: A surface phenomenon where particles from the surface change into the vapor state.

• The rate of evaporation depends on surface area, temperature, humidity, and wind speed.

• Evaporation causes cooling.

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

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

Measurable Quantities and Their Units

• 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)