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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, meaning it takes up space.
- Ancient Understanding of Matter
- Early Indian philosophers believed in “Panch Tatva” – five basic elements: air, earth, fire, sky, and water.
- Ancient Greek philosophers had a similar idea.
- Modern Classification of Matter
- Scientists classify matter based on physical properties and chemical nature.
- This chapter focuses on the physical properties of matter.
1.1 Physical Nature of Matter
1.1.1 Matter is Made Up of Particles
Activity to Understand Particles:
- Fill a beaker halfway with water.
- Dissolve some salt or sugar in the water.
- Observe that the salt/sugar seems to disappear.
- The water level does not change.
- This shows that matter is made up of particles, as the salt/sugar particles fit into the spaces between water particles.
SI Units:
- Mass: kilogram (kg).
- Volume: cubic metre (m³), commonly measured in litres (L).
- 1 L = 1 dm³, 1 L = 1000 mL, 1 mL = 1 cm³.
1.1.2 How Small Are These Particles of Matter?
Activity to Estimate Particle Size:
- Dissolve 2-3 crystals of potassium permanganate in 100 mL of water.
- Take 10 mL of this solution and add it to 90 mL of water, repeating this several times.
- The water remains colored even after many dilutions, showing that particles are very small.
Another Activity Example:
- Using 2 mL of Dettol instead of potassium permanganate.
- The smell of Dettol is detectable even after repeated dilution.
Key Points
- Particles of matter are extremely small.
- They can spread out and mix evenly in water or air.
- Even tiny amounts of substances can affect large volumes, proving the small size of particles.
Characteristics of Particles of Matter
1.2.1 Particles of Matter Have Space Between Them
- Evidence from Activities:
- When sugar, salt, Dettol, or potassium permanganate dissolve in water, they spread out evenly.
- This happens because there is space between the water particles.
- Examples: Making tea, coffee, or lemonade shows particles mixing due to space between them.
1.2.2 Particles of Matter Are Continuously Moving
Activity Examples:
Activity 1.3:
- Unlit incense stick: smell it up close.
- Lit incense stick: smell it from a distance.
Activity 1.4:
- Drop ink in water and observe how it spreads.
- Drop honey in water and observe how it spreads.
Activity 1.5:
Drop crystals of copper sulphate or potassium permanganate in hot and cold water. Observe the rate of spreading.
Conclusions:
- Particles are always moving (kinetic energy).
- Higher temperature makes particles move faster.
- Particles mix on their own (diffusion) and this process is faster when heated.
1.2.3 Particles of Matter Attract Each Other
Activity Examples:
Activity 1.6:
- Form human chains with different strengths of grip.
- Some chains are easier to break than others.
Activity 1.7:
- Try breaking an iron nail, a piece of chalk, and a rubber band.
- Iron nail is hardest to break.
Activity 1.8:
- Try cutting the surface of water with your fingers.
- The water surface stays together.
Conclusions:
- Particles of matter have forces acting between them, keeping them together.
- The strength of this force varies among different materials.
States of Matter
Matter exists in three states: solid, liquid, and gas. These states differ due to the characteristics of their particles.
1.3.1 The Solid State
- Properties of Solids:
- Have a definite shape, distinct boundaries, and fixed volume.
- Negligible compressibility.
- Rigid, meaning they maintain their shape when subjected to force.
Activity 1.9:
- Collect a pen, book, needle, and wooden stick.
- Sketch their shapes and note their properties.
- Observe that solids don’t easily change shape, and are difficult to compress.
Special Cases:
- Rubber Band: Can stretch and regain shape, but breaks under excessive force.
- Sugar and Salt: Take the shape of their container but each crystal retains its 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.
- Flow easily, thus not rigid, but fluid.
Activity 1.10:
- Collect water, oil, milk, juice, and a cold drink.
- Measure 50 mL of liquid and transfer it into different containers.
- Observe that volume remains the same but shape changes.
Diffusion in Liquids:
- Solids and liquids can diffuse into liquids.
- Gases from the atmosphere, like oxygen and carbon dioxide, dissolve in water, helping aquatic life.
- Diffusion is faster in liquids than in solids due to more space between particles.
1.3.3 The Gaseous State
- Properties of Gases:
- Highly compressible.
- No fixed shape or volume.
- Particles move randomly at high speed.
Activity 1.11:
- Use three syringes: one empty, one with water, one with chalk pieces.
- Compress each and observe that gas is easiest to compress.
- Examples:
- LPG cylinders, oxygen cylinders, and CNG in vehicles are compressed gases.
- Smell of food diffuses quickly in air due to high speed and space between gas particles.
- Behavior of Gas Particles:
- Random movement causes particles to hit each other and container walls.
- This creates gas pressure.
These states illustrate the diversity in the physical properties of matter based on particle characteristics.
Can Matter Change Its State?
We know that water can exist in three states:
- Solid (ice)
- Liquid (water)
- Gas (water vapour)
Let’s understand how matter changes its state and what happens to the particles during this change.
1.4.1 Effect of Change of Temperature
Activity 1.12:
- Take 150g of ice in a beaker and insert a thermometer.
- Heat the beaker and note the temperature when ice starts melting and when it completely turns into water.
- Continue heating until the water starts boiling and record observations.
- Observations:
- Heating Solids:
- Increasing temperature increases the kinetic energy of particles.
- Particles vibrate faster, overcome attraction, and move freely.
- Solid melts to become liquid at its melting point.
- Melting Point:
- Temperature at which a solid becomes liquid.
- For ice, the melting point is 273.15 K (0°C).
- The heat absorbed without temperature rise is called latent heat of fusion.
- Heating Solids:
- Heating Liquids:
- Particles move faster and eventually break free from attractions.
- Liquid boils to become gas at its boiling point.
- For water, the boiling point is 373 K (100°C).
- The heat absorbed during boiling without temperature rise is called latent heat of vaporisation.
- Key Points:
- Latent Heat of Fusion: Heat required to change 1 kg of solid to liquid at its melting point.
- Latent Heat of Vaporisation: Heat required to change 1 kg of liquid to gas at its boiling point.
- Particles in steam have more energy than in liquid water at the same temperature due to latent heat.
- Sublimation:
- Some substances change directly from solid to gas and vice versa without becoming liquid.
Activity 1.13:
- Crush camphor in a dish, cover with an inverted funnel, and heat slowly.
- Camphor changes directly to gas, showing sublimation.
Summary
- Matter changes state when temperature changes.
- Solids melt to become liquids (melting point).
- Liquids boil to become gases (boiling point).
- Some substances can sublime, changing directly from solid to gas.
This shows how changing temperature can change the state of matter by affecting the particle movement and energy.
Effect of Change of Pressure
- States of Matter: The states (solid, liquid, gas) differ due to the distances between particles.
- Different states of matter are due to the distances between particles.
- When pressure is applied to a gas in a cylinder, the particles move closer.
- Increasing or decreasing pressure can change the state of matter.
Liquefying Gases
- Solid CO2 (Dry Ice): Stored under high pressure.
- Converts directly from solid to gas when pressure decreases to 1 atmosphere without becoming liquid.
- Pressure and temperature determine if a substance is solid, liquid, or gas.
- Key Point: Both pressure and temperature determine if a substance is solid, liquid, or gas.
- Atmosphere (atm): A unit of pressure.
- 1 atm = 1.01 x 10^5 Pa (Pascals).
- Atmospheric pressure at sea level is 1 atm.
Evaporation
- Everyday Examples of Evaporation:
- Water evaporates when left uncovered.
- Wet clothes dry up.
Understanding Evaporation
- Particles in matter always move.
- Some liquid particles at the surface have enough energy to become vapour.
- Evaporation: The process where a liquid turns into vapour at a temperature below its boiling point.
Factors Affecting Evaporation
Activity to Observe Evaporation
- Take 5 mL of water in different conditions: near a window, under a fan, in a cupboard.
- Record the time taken for evaporation.
Factors
- Surface Area: More surface area means faster evaporation (e.g., spreading clothes to dry).
- Temperature: Higher temperature increases evaporation because particles gain more energy.
- Humidity: Less humidity (less water in the air) means faster evaporation.
- Wind Speed: Higher wind speed helps vapour particles move away, speeding up evaporation.
How Evaporation Causes Cooling
- Energy Absorption: Evaporating particles absorb energy from surroundings, cooling the area.
- Examples:
- Acetone on Palm: Feels cool because it evaporates, taking heat from your skin.
- Sprinkling Water: Cools surfaces after a hot day due to water’s high latent heat of vaporization.
- Cotton Clothes in Summer: Absorb sweat, which then evaporates, cooling the body.
- Condensation Example: Water droplets form on a cold glass because water vapour in the air loses energy and turns into liquid.
Chapter Summary:
- Matter is made up of small particles.
- The matter around us exists in three states—solid, liquid, and gas.
- The forces of attraction between particles are maximum in solids, intermediate in liquids, and minimum in gases.
- The spaces between particles and kinetic energy are minimum in solids, intermediate in liquids, and maximum in gases.
- The arrangement of particles is most ordered in solids, can slip and slide in liquids, and is random in gases.
- The states of matter are inter-convertible by changing temperature or pressure.
- Sublimation is the change of solid state directly to gaseous state without becoming liquid.
- Deposition is the change of gaseous state directly to solid state without becoming liquid.
- Boiling is a bulk phenomenon where particles from the whole liquid change to vapour.
- Evaporation is a surface phenomenon where surface particles gain energy and change to vapour.
- The rate of evaporation depends on surface area, temperature, humidity, and wind speed.
- Evaporation causes cooling.
- Latent heat of vaporisation is the heat energy needed to change 1 kg of liquid to gas at its boiling point.
- Latent heat of fusion is the heat energy needed to change 1 kg of solid to liquid at its melting point.
Measurable Quantities and Units:
- Temperature: kelvin (K)
- Length: metre (m)
- Mass: kilogram (kg)
- Weight: newton (N)
- Volume: cubic metre (m³)
- Density: kilogram per cubic metre (kg/m³)
- Pressure: pascal (Pa)
