.
this is the movement of solute particles from a region of higher concentration to a region of lower concentration.
diffusion can occur in solids, in liquids as well as in gases. It is fastest in gases and slowest in solids
Example of Diffusion
*** When you open a bottle of perfume in one corner of a room, after a short time people in other parts of the room can smell it. (diffusion in gases)
*** If you drop a crystal of potassium permanganate into water, the purple colour slowly spreads through the water without stirring.
That spreading is diffusion (diffusion in liquids)
***When a piece of copper is placed in contact with a piece of zinc and the two metals are heated for a long time, atoms of copper slowly move into the zinc and atoms of zinc move into the copper. After some time, an alloy (brass) is formed (diffusion in solids).
2. BROWNIAN MOTION: - This is the irregular or zigzag movement of small particles in a liquid or gas due to constant collisions with the molecules of the liquid or gas
Example of Brownian Motion
When smoke particles are seen in a beam of sunlight in a dark room, they move about randomly. That movement is also Brownian motion.
3. OSMOSIS: - This is the movement of water molecules from a region of higher concentration to a region of lower concentration through a semi-permeable membrane
4. Evaporation
When water is left in an open container, it slowly changes into vapour even without boiling.
This happens because some water particles are moving fast enough to escape from the liquid into the air.
5. Expansion when heated When a solid, liquid or gas is heated, it expands.
This is because its particles move faster and spread farther apart.
Example:
A heated metal rod becomes longer.
6. Sublimation
Substances like camphor or naphthalene disappear slowly when left in the open.
Their particles move directly from solid to gas because they are in constant motion.
7. Gas pressure
Air inside a balloon push against the walls of the balloon.
This is due to continuous movement and collision of gas particles.
Change of State
A change of state is the physical process by which a substance changes from one state of matter to another without any change in its chemical composition. These changes occur as a result of gain or loss of heat energy, which affects the kinetic energy of the particles.
According to the kinetic theory of matter, all matter is made up of tiny particles that are in constant motion. The speed of these particles determines the state of matter.
Types of Change of State
1. Melting (Solid → Liquid)
Melting occurs when a solid is heated and changes into a liquid. Heat energy supplied increases the kinetic energy of the particles, causing them to vibrate more rapidly until they overcome the forces holding them together.
Example: Ice melting into water.
2. Freezing (Liquid → Solid)
Freezing is the change of a liquid into a solid when heat is removed. The particles lose kinetic energy and become fixed in position.
Example: Water freezing to form ice.
3. Boiling / Vaporization (Liquid → Gas)
Boiling occurs when a liquid changes into a gas at a fixed temperature called the boiling point. At this point, particles gain enough kinetic energy to escape from the liquid.
Example: Water changing to steam at 100°C.
4. Condensation (Gas → Liquid)
Condensation occurs when a gas loses heat and changes into a liquid. The particles lose kinetic energy and move closer together.
Example: Water droplets forming on a cold surface.
5. Sublimation (Solid → Gas)
Sublimation is the direct change of a solid into a gas without passing through the liquid state.
Examples: Iodine, naphthalene, and dry ice.
6. Deposition (Gas → Solid)
Deposition is the direct change of a gas into a solid without passing through the liquid state.
Example: Frost formation.
Role of Heat Energy
Important Exam Points
Change of state is a physical change.
No new substance is formed.
Temperature remains constant during change of state until the process is complete.
Explained using kinetic energy of particles.
OBJECTIVE QUESTIONS
1. The kinetic theory of matter states that matter is made up of
A. ions
B. molecules
C. tiny particles
D. compounds
2. According to the kinetic theory, particles of matter are always
A. at rest
B. vibrating only
C. in constant motion
D. fixed in position
3. Which of the following best explains diffusion?
A. Attraction between particles
B. Movement of particles from high to low concentration
C. Chemical reaction
D. Expansion of solids
4. Brownian motion is caused by
A. gravity
B. heat
C. collision of molecules
D. evaporation
5. Which state of matter has particles that are far apart and move freely?
A. Solid
B. Liquid
C. Gas
D. Plasma
6. The force of attraction between particles is strongest in
A. gases
B. liquids
C. solids
D. vapour
7. When a solid is heated, its particles
A. stop moving
B. move faster
C. move closer
D. disappear
8. Which of the following shows that gas particles are in motion?
A. Crystallization
B. Diffusion of gas
C. Freezing
D. Condensation
9. The random movement of smoke particles in air is called
A. diffusion
B. evaporation
C. Brownian motion
D. osmosis
10. The kinetic energy of particles increases when
A. temperature decreases
B. temperature increases
C. pressure decreases
D. volume decreases
11. In which state of matter do particles vibrate about fixed positions?
A. Gas
B. Liquid
C. Solid
D. Vapour
12. Osmosis occurs because of
A. random motion of particles
B. chemical reaction
C. evaporation
D. heating
13. Which of the following best describes particles in a liquid?
A. Fixed and tightly packed
B. Far apart and free
C. Close together and able to move
D. Completely motionless
14. The spreading of perfume in a room is due to
A. osmosis
B. diffusion
C. evaporation
D. freezing
15. The kinetic theory explains that gas pressure is due to
A. weight of gas
B. collisions of particles with container walls
C. chemical reactions
D. gravity
16. Which of these is evidence that particles of matter are in motion?
A. Expansion when heated
B. Rusting
C. Burning
D. Melting
17. When temperature increases, the average kinetic energy of particles
A. decreases
B. remains constant
C. increases
D. becomes zero
18. Particles in a gas have
A. very strong forces of attraction
B. weak forces of attraction
C. no energy
D. fixed positions
19. Diffusion occurs fastest in
A. solids
B. liquids
C. gases
D. crystals
20. The kinetic theory of matter is used to explain
A. chemical reactions
B. structure of atoms
C. behaviour of solids, liquids and gases
D. electricity
region of lower concentration through a semi permeable membrane.
