Matter In Our Surroundings

Matter is anything that occupies space and has mass. Early Indian philosophers classified matter into Panch Tatva (air, earth, fire, sky, water).

Modern classification is based on:

• Physical properties
• Chemical nature

Matter is made up of particles

• Observation: When sugar/salt dissolves in water, the water level does not rise significantly.
• Inference: This indicates that the particles of sugar/salt occupy the spaces between the particles of water.
• Conclusion: Matter is not continuous but particulate in nature.

How small are these particles?

• Activity: Dilution of potassium permanganate solution (or Dettol).
• A few crystals of potassium permanganate can colour a large volume of water (e.g., 1000 L).
• Repeated dilution (e.g., 5-8 times) still shows colour/smell.
• Conclusion: Particles of matter are extremely small, beyond our imagination, and they keep dividing into smaller units.

Particles of matter exhibit three main characteristics:

1. Particles of matter have space between them

• Evidence:
• Dissolution of salt/sugar in water (Activity 2.1).
• Intermixing of ink/honey in water (Activity 2.4) – ink spreads faster than honey due to weaker intermolecular forces and smaller particle size.
• Explanation: The particles of one substance get into the spaces between the particles of the other.

2. Particles of matter are continuously moving

• Evidence:
• Smell of an unlit incense stick (Activity 2.3) – smell is felt only when close.
• Smell of a lit incense stick (Activity 2.3) – smell spreads faster and is felt from a distance.
• Spreading of ink in water (Activity 2.4).
• Diffusion of copper sulphate/potassium permanganate in water (Activity 2.5).
• Explanation: Particles possess kinetic energy. As temperature increases, kinetic energy increases, leading to faster movement.
• Diffusion: The intermixing of particles of two different types of matter on their own due to particle movement. Rate of diffusion increases with temperature.

3. Particles of matter attract each other

• Evidence:
• Breaking a human chain (Activity 2.6): Easier to break chains with loose holds (fingertips) than tight holds (locked arms), indicating varying forces of attraction.
• Breaking an iron nail, cardboard, rubber band (Activity 2.7): Iron nail is hardest to break, rubber band is stretchable, cardboard can be cut. This shows different strengths of forces.
• Cutting water surface with fingers (Activity 2.8): Easy to cut water, but particles still hold together, showing weaker forces compared to solids.
• Explanation: There is a force of attraction between particles that keeps them together. The strength of this force varies significantly between different types of matter.

Matter exists in three main states: Solid, Liquid, and Gas. These states are due to the varying strength of intermolecular forces of attraction and the arrangement of particles.

The Solid State

• Properties:
• Definite shape and fixed volume.
• Distinct boundaries.
• Rigid and incompressible (negligible compressibility).
• Particles are tightly packed and vibrate about their fixed positions.
• Cannot diffuse into each other easily.
• Examples: Pen, book, iron nail, sugar, salt, wood.
• Exceptions/Special Cases:
• Rubber band: Changes shape under force but regains original shape when force is removed. It breaks if excessive force is applied. It is considered a solid because it has a definite shape unless stretched.
• Sugar/Salt crystals: Individual crystals have a fixed shape, even if the bulk takes the shape of the container.
• Sponge: Has minute holes trapping air. When pressed, air is expelled, allowing compression. Still considered a solid due to its definite structure.

The Liquid State

• Properties:
• No definite shape (takes shape of container).
• Fixed volume.
• Not rigid, but fluid (can flow).
• Particles are less tightly packed than solids, can slide over each other.
• Moderately compressible.
• Diffusion is faster than in solids.
• Examples: Water, milk, oil, juice.
• Aquatic life: Aquatic animals and plants can survive in water because dissolved oxygen (a gas) diffuses into water.

The Gaseous State

• Properties:
• No definite shape (takes shape of container).
• No fixed volume (occupies entire volume of container).
• Highly compressible.
• Highly fluid (particles move randomly and rapidly).
• Particles are far apart with weak forces of attraction.
• High rate of diffusion.
• Exerts pressure on the walls of the container due to random collision of particles.
• Examples: Air, oxygen, LPG, CNG.
• Applications of high compressibility:
• LPG (Liquefied Petroleum Gas): Used for cooking, stored in cylinders.
• CNG (Compressed Natural Gas): Used as fuel in vehicles.
• Oxygen cylinders: Supplied to hospitals.
• Large volumes of gas can be compressed into small cylinders for easy transport.
• Smell of food: The aroma particles of food mix rapidly with air particles and spread quickly due to high kinetic energy and large spaces between gas particles.

Matter can change its state by changing temperature. For example, water exists as ice (solid), water (liquid), and water vapour (gas).

Solid to Liquid (Melting/Fusion)

• Process: On heating a solid, particles gain kinetic energy, vibrate more vigorously, overcome forces of attraction, and leave fixed positions to move freely.
• Melting Point: The minimum temperature at which a solid melts to become a liquid at atmospheric pressure. It indicates the strength of intermolecular forces.
• Melting point of ice = 0°C or 273.15 K.
• Latent Heat of Fusion: The amount of heat energy required to change 1 kg of a solid into liquid at its melting point, without any change in temperature.
• During melting, the temperature remains constant even though heat is supplied. This heat is used to overcome the forces of attraction between particles.

Liquid to Gas (Boiling/Vaporisation)

• Process: On heating a liquid, particles gain enough energy to break free from the attractive forces and convert into gas.
• Boiling Point: The temperature at which a liquid starts boiling at atmospheric pressure.
• Boiling point of water = 100°C or 373 K (273 + 100).
• Latent Heat of Vaporisation: The amount of heat energy required to change 1 kg of a liquid into gas at its boiling point, without any change in temperature.
• Steam at 100°C has more energy than water at 100°C due to the latent heat of vaporisation absorbed.

Gas to Liquid (Condensation)

• Process: Cooling a gas reduces the kinetic energy of particles, they come closer, and forces of attraction become strong enough to form a liquid.

Liquid to Solid (Freezing/Solidification)

• Process: Cooling a liquid reduces kinetic energy, particles come closer, and arrange into fixed positions.

Temperature Conversion:

• Celsius to Kelvin: K = °C + 273.15 (often rounded to 273)
• Kelvin to Celsius: °C = K - 273.15 (often rounded to 273)

Sublimation

• Definition: The direct change of state from solid to gas without passing through the liquid state.
• Examples: Camphor, ammonium chloride, iodine, naphthalene balls, dry ice (solid CO₂).
• Activity (2.13): Heating ammonium chloride in a china dish with an inverted funnel. Solid ammonium chloride directly converts to vapours, which then cool and deposit as solid on the cooler inner walls of the funnel.

Deposition

• Definition: The direct change of state from gas to solid without passing through the liquid state.
• Example: Vapours of ammonium chloride depositing as solid on cooling.

Pressure also plays a significant role in changing the state of matter, especially for gases.

• Gases to Liquids (Liquefaction):
• Applying pressure on a gas brings its particles closer.
• If enough pressure is applied and temperature is lowered, the gas particles come so close that the forces of attraction become strong enough to convert the gas into a liquid.
• This process is called condensation (when referring to gas to liquid by cooling) or liquefaction (when referring to gas to liquid by pressure/cooling).
• Example: LPG and CNG are stored as liquids under high pressure.

• Solid CO₂ (Dry Ice):
• Solid carbon dioxide is stored under high pressure.
• When pressure is decreased to 1 atmosphere (atm), it directly converts to gaseous CO₂ without melting.
• This is why it's called dry ice – it doesn't leave any liquid residue.
• This is an example of sublimation.

• Conclusion: Both temperature and pressure determine the state of matter.

Evaporation

• Definition: A surface phenomenon in which liquid changes into vapour at any temperature below its boiling point.
• Mechanism: Particles at the surface of the liquid, having higher kinetic energy, overcome the forces of attraction of other particles and escape into the atmosphere as vapour.

Factors Affecting Evaporation

1. Surface Area:

• Increase in surface area = Increase in rate of evaporation.
• Reason: More surface particles are exposed to the atmosphere, increasing the chance of escaping.
• Example: Clothes dry faster when spread out.

1. Temperature:

• Increase in temperature = Increase in rate of evaporation.
• Reason: Higher temperature provides more kinetic energy to particles, making it easier for them to overcome attractive forces and escape.
• Example: Clothes dry faster on a sunny day.

1. Humidity:

• Increase in humidity = Decrease in rate of evaporation.
• Reason: Humidity is the amount of water vapour already present in the air. If the air already has a lot of water vapour, its capacity to hold more water vapour decreases, slowing down evaporation.
• Example: Clothes dry slower on a humid (rainy) day.

1. Wind Speed:

• Increase in wind speed = Increase in rate of evaporation.
• Reason: Increased wind speed carries away the water vapour particles from the surface of the liquid, decreasing the concentration of water vapour in the surroundings and thus increasing the rate of evaporation.
• Example: Clothes dry faster on a windy day.

• Mechanism: During evaporation, particles at the surface of the liquid absorb energy from the surroundings to overcome the forces of attraction and change into vapour.
• Energy source: This absorbed energy (latent heat of vaporisation) is taken from the liquid itself and its surroundings.
• Result: When energy is removed from the surroundings, the surroundings feel cool.

Everyday Examples of Cooling by Evaporation:

1. Acetone/Spirit on palm: When you put acetone or spirit on your palm, it evaporates quickly, absorbing heat from your palm, making it feel cool.
2. Earthen pots (Matka): Water stored in earthen pots remains cool. The pot has tiny pores through which water seeps out to the surface and evaporates. This evaporation absorbs latent heat from the remaining water inside, cooling it.
3. Sweating: Our body produces sweat to cool down. When sweat evaporates from the skin, it absorbs heat from the body, leading to a cooling sensation.
4. Desert Coolers: On a hot dry day, a desert cooler works effectively. The fan draws hot dry air through water-soaked pads. The water evaporates, cooling the air, which is then circulated into the room.
5. Sprinkling water on roofs: People sprinkle water on the ground or roofs after a hot day. The water evaporates, absorbing heat from the surface and cooling it down.
6. Cotton clothes in summer: Cotton is a good absorber of water. It absorbs sweat and exposes it to the atmosphere for easy evaporation. This evaporation causes cooling, making us feel comfortable.