Chemistry · Class 9-10 · CBSE
States of Matter, Latent Heat and Mixtures
Explore particle theory of matter, comparison of solids/liquids/gases, latent heat of fusion & vaporisation, evaporative cooling, homogeneous vs heterogeneous mixtures, and true solutions vs colloids vs suspensions.
1Kinetic Particle Nature of Matter
Matteris anything that has mass and occupies volume. Particulate theory states that matter is composed of tiny particles that possess kinetic energy, move continuously, and exert inter-particle forces of attraction.
Solid vs Liquid vs Gas: Kinetic Molecular Comparison
| Characteristic | Solids | Liquids | Gases |
|---|---|---|---|
| Inter-particle Distance | Extremely small / closely packed | Intermediate spacing | Very large random distances |
| Inter-particle Attraction | Maximum | Intermediate | Negligible / minimum |
| Kinetic Energy | Minimum (vibrate about mean position) | Intermediate | Maximum (rapid random chaotic motion) |
| Shape and Volume | Definite shape and fixed volume | No fixed shape; takes container shape; fixed volume | No fixed shape and no fixed volume (fills container) |
| Compressibility | Negligible (almost incompressible) | Very low | Highly compressible (e.g. CNG, LPG cylinders) |
| Fluidity & Diffusion | Do not flow; diffusion is extremely slow | Flows from higher to lower level; moderate diffusion | Flows in all directions; diffuses rapidly |
Inter-particle Distance
- Solids
- Extremely small / closely packed
- Liquids
- Intermediate spacing
- Gases
- Very large random distances
Inter-particle Attraction
- Solids
- Maximum
- Liquids
- Intermediate
- Gases
- Negligible / minimum
Kinetic Energy
- Solids
- Minimum (vibrate about mean position)
- Liquids
- Intermediate
- Gases
- Maximum (rapid random chaotic motion)
Shape and Volume
- Solids
- Definite shape and fixed volume
- Liquids
- No fixed shape; takes container shape; fixed volume
- Gases
- No fixed shape and no fixed volume (fills container)
Compressibility
- Solids
- Negligible (almost incompressible)
- Liquids
- Very low
- Gases
- Highly compressible (e.g. CNG, LPG cylinders)
Fluidity & Diffusion
- Solids
- Do not flow; diffusion is extremely slow
- Liquids
- Flows from higher to lower level; moderate diffusion
- Gases
- Flows in all directions; diffuses rapidly
2Interconversion of States and Latent Heat
Latent Heatis the hidden thermal energy absorbed or released by a substance during a change of state without any change in its temperature.
Latent Heat Types & Thermal Phenomena
| Concept | Scientific Definition | Quantitative Value for Water | Physical Consequence |
|---|---|---|---|
| Latent Heat of Fusion | Heat required to change 1 kg solid to liquid at melting point | 3.34 × 10⁵ J/kg | Ice at 0°C cools more effectively than water at 0°C because ice absorbs latent heat |
| Latent Heat of Vaporisation | Heat required to change 1 kg liquid to gas at boiling point | 22.6 × 10⁵ J/kg | Steam at 100°C causes far more severe burns than boiling water at 100°C |
| Sublimation | Direct transition from solid to gas without entering liquid phase | Examples: Camphor, Ammonium Chloride (NH₄Cl), Naphthalene, Dry Ice (solid CO₂) | Purification of sublimable solids from non-sublimable impurities |
Latent Heat of Fusion
- Scientific Definition
- Heat required to change 1 kg solid to liquid at melting point
- Quantitative Value for Water
- 3.34 × 10⁵ J/kg
- Physical Consequence
- Ice at 0°C cools more effectively than water at 0°C because ice absorbs latent heat
Latent Heat of Vaporisation
- Scientific Definition
- Heat required to change 1 kg liquid to gas at boiling point
- Quantitative Value for Water
- 22.6 × 10⁵ J/kg
- Physical Consequence
- Steam at 100°C causes far more severe burns than boiling water at 100°C
Sublimation
- Scientific Definition
- Direct transition from solid to gas without entering liquid phase
- Quantitative Value for Water
- Examples: Camphor, Ammonium Chloride (NH₄Cl), Naphthalene, Dry Ice (solid CO₂)
- Physical Consequence
- Purification of sublimable solids from non-sublimable impurities
Factors Governing Evaporation and Evaporative Cooling
- 1
1. Surface Area: Evaporation is a surface phenomenon. Increasing surface area increases evaporation rate (e.g. spreading clothes to dry).
- 2
2. Temperature: Higher temperature increases kinetic energy, enabling more surface molecules to escape into vapour.
- 3
3. Humidity: High humidity in air lowers evaporation rate (sweat does not evaporate easily on humid monsoon days).
- 4
4. Wind Speed: Strong wind sweeps away vapour particles, increasing evaporation rate.
- 5
5. Evaporative Cooling Principle: Escaping energetic molecules absorb latent heat from surroundings, lowering surrounding temperature (e.g. earthen pot / matka cooling water).
3True Solutions vs Colloids vs Suspensions
Comparison of Solution Types
| Property | True Solution | Colloid | Suspension |
|---|---|---|---|
| Particle Size | < 1 nm (10⁻⁹ m) | 1 nm to 1000 nm | > 1000 nm (10⁻⁶ m) |
| Homogeneity | Homogeneous mixture | Heterogeneous (looks homogeneous) | Heterogeneous mixture |
| Stability | Very stable (particles do not settle) | Stable (particles do not settle on standing) | Unstable (particles settle at bottom over time) |
| Tyndall Effect (Light Scattering) | Does NOT scatter light (path of beam invisible) | Shows strong Tyndall effect (path of beam visible) | Shows Tyndall effect until particles settle down |
| Filtration Separation | Passes through filter paper and membrane | Passes through filter paper; separated by centrifugation | Separated easily by ordinary filter paper |
| Everyday Examples | Salt water, sugar solution, copper sulphate in water | Milk, blood, ink, fog, clouds, smoke | Chalk powder in water, muddy water, sand in water |
Particle Size
- True Solution
- < 1 nm (10⁻⁹ m)
- Colloid
- 1 nm to 1000 nm
- Suspension
- > 1000 nm (10⁻⁶ m)
Homogeneity
- True Solution
- Homogeneous mixture
- Colloid
- Heterogeneous (looks homogeneous)
- Suspension
- Heterogeneous mixture
Stability
- True Solution
- Very stable (particles do not settle)
- Colloid
- Stable (particles do not settle on standing)
- Suspension
- Unstable (particles settle at bottom over time)
Tyndall Effect (Light Scattering)
- True Solution
- Does NOT scatter light (path of beam invisible)
- Colloid
- Shows strong Tyndall effect (path of beam visible)
- Suspension
- Shows Tyndall effect until particles settle down
Filtration Separation
- True Solution
- Passes through filter paper and membrane
- Colloid
- Passes through filter paper; separated by centrifugation
- Suspension
- Separated easily by ordinary filter paper
Everyday Examples
- True Solution
- Salt water, sugar solution, copper sulphate in water
- Colloid
- Milk, blood, ink, fog, clouds, smoke
- Suspension
- Chalk powder in water, muddy water, sand in water
4Exam Corner: Tips, Mistakes & Board Questions
Exam High-Yield Revision Points
- Temperature in Kelvin = Temperature in Celsius + 273.15 (0°C = 273 K).
- Dry Ice is solid carbon dioxide (CO₂) stored under high pressure. On decreasing pressure to 1 atm, it sublimes directly into gas without melting.
- Centrifugation uses rapid spinning to force denser particles to bottom and lighter particles to top; used in diagnostic blood/urine labs and dairy butter churning.
Exam question · CBSE Class 9/10 Board
- A.Because steam has lower density
- B.Because steam particles possess extra latent heat of vaporisation (22.6 × 10⁵ J/kg) at the same temperature
- C.Because water conducts heat poorly
- D.Because steam contains chemical toxins
- Both steam and boiling water are at 100°C.
- However, 1 kg of steam contains an additional 22.6 × 10⁵ Joules of latent heat of vaporisation absorbed during phase change.
- When steam condenses on skin, it delivers this extra heat before cooling down as water, causing severe deep burns.
- Correct answer is option B.
Answer: B. Because steam particles possess extra latent heat of vaporisation (22.6 × 10⁵ J/kg) at the same temperature
Remember
- Particles of matter possesskinetic energyand mutualinter-particle attraction.
- Latent Heatdrives phase transitions without raising temperature.
- Evaporative coolinghappens because escaping energetic molecules take away heat from the surface.
- Colloidshave particle size between 1 nm and 1000 nm and scatter light via theTyndall effect.
Check yourself
Question 1
Which of the following processes is used to separate butter from curd or cream in dairies?