Melting: Solid → Liquid (Heat absorbed at melting point)
Freezing: Liquid → Solid (Heat released at freezing point)
Vaporization: Liquid → Gas (Heat absorbed at boiling point)
Condensation: Gas → Liquid (Heat released)
Sublimation: Solid → Gas directly (e.g., dry ice, camphor)
Deposition: Gas → Solid directly (e.g., frost formation)
Important Temperatures: Ice melts at 0°C | Water boils at 100°C | Room temperature ~25°C
Change of State
From → To
Heat Exchange
Example
Temperature
Melting
Solid → Liquid
Heat absorbed
Ice to water
0°C (for ice)
Freezing
Liquid → Solid
Heat released
Water to ice
0°C (for water)
Boiling
Liquid → Gas
Heat absorbed
Water to steam
100°C (for water)
Condensation
Gas → Liquid
Heat released
Steam to water
100°C (for steam)
Sublimation
Solid → Gas
Heat absorbed
Dry ice to CO₂
-78°C (for dry ice)
Diffusion and Brownian Motion
Diffusion: The spontaneous mixing of particles of different substances when they are in contact. It occurs in all three states but is fastest in gases.
Examples of Diffusion:
• Perfume spreading in air
• Tea bag coloring water
• Sugar dissolving in water
• Ink spreading in water
• Smell of cooking food
💫 DIFFUSION RATES 💫
Speed of Diffusion:
🏃♂️ GASES: Fastest (particles move freely)
🚶♂️ LIQUIDS: Medium (particles slide past each other)
🐌 SOLIDS: Slowest (particles only vibrate)
Brownian Motion: The random zigzag movement of small particles suspended in a fluid (liquid or gas) due to collision with fast-moving particles of the fluid.
Factors affecting Diffusion:
• Temperature (higher temperature = faster diffusion)
• Size of particles (smaller particles = faster diffusion)
• State of matter (gas > liquid > solid)
• Concentration gradient (greater difference = faster diffusion)
Properties of Matter
Property
Solid
Liquid
Gas
Shape
Fixed/Definite
No fixed shape
No fixed shape
Volume
Fixed/Definite
Fixed/Definite
No fixed volume
Compressibility
Negligible
Very slight
Highly compressible
Density
High
Medium
Low
Kinetic Energy
Least
Medium
Maximum
Intermolecular Forces
Very strong
Moderate
Very weak
Particle Movement
Vibrational only
Vibrational + Rotational
Random motion
Physical and Chemical Changes
Physical Changes
Definition: Changes that affect only the physical properties of matter. No new substance is formed.
Examples:
• Melting of ice
• Boiling of water
• Dissolution of salt
• Cutting of paper
• Magnetization of iron
Characteristics:
• Reversible
• No new substance formed
• Molecular composition unchanged
• Energy change is small
Chemical Changes
Definition: Changes that result in formation of new substances with different properties. Molecular composition changes.
Examples:
• Burning of paper
• Rusting of iron
• Digestion of food
• Photosynthesis
• Cooking of food
Characteristics:
• Usually irreversible
• New substances formed
• Molecular composition changes
• Large energy changes
⚠️ Important Note: State changes (melting, boiling, freezing) are physical changes because the chemical composition remains the same. Only the arrangement of particles changes.
Section B: Short Answer Questions
Q1. Define matter and state its characteristics.
Answer: Matter is anything that occupies space and has mass. Characteristics: Made of particles, particles are in constant motion, particles have kinetic energy, intermolecular forces exist between particles.
Q2. Name the three states of matter and give two examples of each.
Answer: Solid (ice, wood), Liquid (water, oil), Gas (air, oxygen). Each state has different particle arrangement and energy levels.
Q3. What is diffusion? Give three examples.
Answer: Diffusion is spontaneous mixing of particles of different substances. Examples: Perfume spreading in air, sugar dissolving in water, ink mixing with water.
Q4. Distinguish between melting and boiling.
Answer: Melting: Solid to liquid at fixed temperature (melting point). Boiling: Liquid to gas at fixed temperature (boiling point) with bubble formation throughout the liquid.
Q5. What is sublimation? Give two examples.
Answer: Sublimation is direct change from solid to gas without passing through liquid state. Examples: Dry ice (solid CO₂), camphor, iodine crystals.
Q6. Why do gases have no fixed shape or volume?
Answer: Gas particles have high kinetic energy, move randomly in all directions, have weak intermolecular forces, and are widely separated. They fill any container completely.
Q7. What is Brownian motion?
Answer: Brownian motion is random zigzag movement of small particles suspended in fluid due to collision with fast-moving fluid particles. Proves particle nature of matter.
Q8. Why is ice lighter than water?
Answer: Ice has crystalline structure with more space between particles than liquid water, making it less dense. Hence ice floats on water.
Q9. What factors affect the rate of diffusion?
Answer: Temperature (higher temperature increases rate), particle size (smaller particles diffuse faster), state of matter (gases > liquids > solids), concentration gradient.
Q10. Distinguish between physical and chemical changes.
Answer: Physical changes: No new substance formed, reversible, composition unchanged (melting ice). Chemical changes: New substances formed, usually irreversible, composition changes (burning paper).
Section C: Long Answer Questions
Q1. Explain the kinetic theory of matter and how it relates to the three states of matter.
Solution: Kinetic theory states that all matter consists of tiny particles in constant motion. Particle movement determines state: solids have particles vibrating in fixed positions with strong intermolecular forces, liquids have particles sliding past each other with moderate forces, gases have particles moving randomly with weak forces. Higher temperature increases kinetic energy and particle movement, causing state changes.
Q2. Describe the process of diffusion and factors affecting its rate.
Solution: Diffusion is spontaneous mixing of particles of different substances. Rate depends on: temperature (higher temperature = faster diffusion due to increased kinetic energy), particle size (smaller particles diffuse faster), state of matter (gases > liquids > solids due to particle freedom), concentration gradient (greater difference = faster rate). Examples: perfume spreading in air, tea coloring water, sugar dissolving completely.
Q3. Compare and contrast the properties of solids, liquids, and gases.
Solution: Solids: fixed shape and volume, high density, incompressible, strong intermolecular forces, particles vibrate in fixed positions. Liquids: fixed volume but no fixed shape, medium density, slightly compressible, moderate forces, particles slide past each other. Gases: no fixed shape or volume, low density, highly compressible, weak forces, particles move randomly in all directions filling entire container.
Q4. Explain the different changes of state with examples and energy changes involved.
Solution: Changes of state are physical processes: Melting (solid→liquid): ice to water at 0°C, heat absorbed to break intermolecular bonds. Freezing (liquid→solid): water to ice, heat released as bonds form. Vaporization (liquid→gas): water to steam at 100°C, heat absorbed to overcome attractions. Condensation (gas→liquid): steam to water, heat released. Sublimation (solid→gas): dry ice to CO₂, heat absorbed. All maintain chemical composition.
Q5. Distinguish between physical and chemical changes with detailed examples and characteristics.
Solution: Physical changes: no new substances formed, usually reversible, molecular composition unchanged, small energy changes. Examples: melting ice (H₂O remains H₂O), boiling water, dissolving salt (ions separate but don't change), cutting paper. Chemical changes: new substances formed with different properties, usually irreversible, molecular composition changes, large energy changes. Examples: burning paper (forms ash, CO₂, H₂O), rusting iron (Fe becomes Fe₂O₃), digestion (breaks complex molecules into simple ones), photosynthesis.
Q6. Explain Brownian motion and its significance in understanding particle theory.
Solution: Brownian motion is random zigzag movement of small particles suspended in fluid due to collision with fast-moving fluid particles. Discovered by Robert Brown in 1827. Significance: provides direct evidence for kinetic theory, proves particles are in constant motion, demonstrates molecular bombardment, shows temperature affects particle movement. Visible under microscope with pollen grains in water or smoke particles in air.
Q7. Describe the arrangement and motion of particles in different states of matter.
Solution: Solids: particles arranged in regular, fixed patterns (crystalline structure), held together by strong forces, only vibrational motion about fixed positions, closely packed with minimum empty space. Liquids: particles irregularly arranged but still close, moderate intermolecular forces, vibrational and translational motion allowing flow, some empty space. Gases: particles widely separated with maximum empty space, weak intermolecular forces, rapid random motion in all directions, particles independent of each other.
Q8. Explain why ice floats on water and relate this to particle arrangement.
Solution: Ice floats on water because it is less dense than liquid water. In ice, water molecules form a rigid crystalline structure with hexagonal arrangements, creating more space between molecules compared to liquid water where molecules are more closely packed and can move freely. The ice structure has density ~0.92 g/cm³ while liquid water has density 1.0 g/cm³. This unusual property is crucial for aquatic life survival during winter as ice forms an insulating layer on water surfaces.