Course:
Chemistry - 0570
This lesson introduces the particulate nature of matter and explains that all matter is made up of extremely small particles such as atoms and molecules. The arrangement, movement and energy of these particles determine the physical state of matter.
Learners will study the three main states of matter: solids, liquids and gases, and explain them using the Kinetic Particle Theory. The lesson also explains how matter changes state when heat energy is added or removed. In addition, learners will explore diffusion, the process by which particles move from regions of high concentration to regions of low concentration.
Practical demonstrations of diffusion in gases help learners understand how molecular mass affects the rate of diffusion.
All matter is composed of tiny particles called atoms, molecules or ions.
• are extremely small
• are in constant motion
• have spaces between them
• attract each other with intermolecular forces
The behaviour of these particles is explained by the Kinetic Particle Theory.
• Solid
• Liquid
• Gas
The differences between these states depend on particle arrangement, movement and forces of attraction.
Particle arrangement
Particles are tightly packed together in a fixed and orderly arrangement.
Particle movement
Particles cannot move freely but vibrate about fixed positions.
• definite shape
• definite volume
• not easily compressible
• particles have strong forces of attraction
Examples include iron, salt, wood and ice.
Particle arrangement
Particles are close together but arranged randomly.
Particle movement
Particles move and slide past one another.
• definite volume
• no definite shape (take the shape of the container)
• able to flow
• slightly compressible
Examples include water, oil and alcohol.
Particle arrangement
Particles are very far apart with large spaces between them.
Particle movement
Particles move rapidly and randomly in all directions.
• no definite shape
• no definite volume
• easily compressed
• weak forces of attraction between particles
Examples include oxygen, nitrogen and carbon dioxide.
Changes of state occur when heat energy is added or removed from matter.
• particles gain kinetic energy
• particles move faster
• particles move further apart
• particles lose kinetic energy
• particle movement slows down
• particles move closer together
Common changes of state include:
Example:
Ice melts into water when heated and water boils to form steam when further heated.
Diffusion is the movement of particles from a region of high concentration to a region of low concentration.
• gases
• liquids
Diffusion happens because particles are constantly moving randomly.
Example
When perfume is sprayed in a room, the smell spreads throughout the room due to diffusion of gas particles.
The rate at which diffusion occurs depends on several factors:
• molecular mass
• temperature
• concentration difference
Particles with lower molecular mass diffuse faster than heavier particles.
For example, ammonia gas diffuses faster than hydrogen chloride gas because ammonia molecules are lighter.
A common experiment involves ammonia gas and hydrogen chloride gas placed at opposite ends of a long glass tube.
As the gases diffuse toward each other, a white ring of ammonium chloride forms where they meet.
The ring forms closer to the hydrogen chloride end because ammonia molecules diffuse faster.
This experiment demonstrates how molecular mass affects diffusion rate.
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