Kinetic Particle Theory

Physical Change
- NO new substance formed.
- Usually easily reversible.
- May or may not involve heating
- Some types of physical changes include

1.     Grinding, tearing cutting or shaping

2.  A change of state or phase from a solid to liquid.

Chemical Change
-  New chemical substance(s) is/are formed
- Usually irreversible (Some chemical change can be reversed under special conditions)
- Heat energy may be given off or absorbed
- Light energy may be given off or absorbed

Signs of a chemical change

- A change in colour

- Production of a gas

- Formation of a precipitate from mixing solutions

- Change of temperature

All of the above must follow the formation of a new chemical substance

Chemical reactions

- A process in which new chemical substances are formed

Eg.    A+B   ->   C+D

    Reactants -> Products

- New chemical substances formed due to rearrangement of atoms

- No atoms are created or destroyed, according to le Law of Constant Mass

Types of chemical reactions:

B     Combination (Synthesis)

~ Two or more substances combine to form a new substance

~ Eg. Magnesium + oxygen -> magnesium oxide

B     Decomposition

~ A substance breaks down into two or more simpler substances

B     Combustion or burning

~ Combination of a substance with oxygen

~ Heat and light energy are given off

~ Eg. Hydrocarbon + oxygen -> carbon dioxide + water

B     Displacement reaction

~ A chemical reaction with an atom/ a group of atoms that got replaced by another atom/group of atoms

~ Eg. Hydrogen bromide -> hydrogen chloride + bromine

Analogy to explain Kinetic Particle Theory

Example 1

A rock concert to illustrate interconversion of solid (during concert)to liquid (after concert ends) - melting


Features similar to kinetic particle model
- During concert, people are closely packed & jumping at fixed positions, just like particle in solid state
- When concert ends, people are moving disorderly sliding past each other but still closely packed, just like particles in liquid state

Assumptions:
- People are large in numbers yet small in size relative to entire concert hall. 
- People do not stick to each other upon collision.
- Each person possess kinetic energy.
- Each person moves in constant and random motion. 

Limitations:
- People are of different sizes/masses unlike particles which are of same size/mass of same substance.
- There is no force of attraction between people unlike particles which consist strong forces of attraction between them.
- People are not standing in ordered arrangement, unlike particles in solid state in ordered arrangement. 


Example 2

Soccer Match to illustrate interconversion of solid to liquid to gas

Explanation: The soccer players stand together at first like a solid, and it becomes like liquid when they take their positions on the field, then gas when they start running around.

Assumptions:
- The soccer players do not stick to each other upon collision
- The soccer players posses kinetic energy

Limitations:
- The soccer players are of different masses and sizes
- There are no forces of attraction between the players
- The players might stop moving to rest for a while, unlike particles which are in constant random motion

Example 3

ATM queuing to illustrate diffusion in liquid

Explanation:
Liquid diffuses from a region of higher concentration to a region of lower concentration, like how people naturally choose the shortest line to stand in.

Assumptions:
- People do not stick to each other upon collision
- The people posses kinetic energy

Limitations:
- The people who are queuing are of different masses and sizes
- While waiting for their turn, the people do not move anywhere until the person in front finishes withdrawing money from the ATM, unlike particles which are in constant random motion.
- There are no forces of attraction between the people

Example 4

Comparing animals in cage and wildlife to illustrate sublimation 

Explanation:
In cages, the animals are packed tightly and in an orderly manner, like a solid. When they are released into the wild, they disperse and become like gas. The animals are also constantly moving when they are awake, like particles.

Assumptions:
- The animals do not stick to each other upon collision
- The animals posses kinetic energy

Limitations:
- The animals are not all of the same size or mass
- When the animals are resting or sleeping, they are not moving, unlike particles which are always in constant random motion.

Kinetic Particle Theory

The theory states that all matter is made of tiny particles and that all these particles are in constant, random motion

Assumptions made:

- All matter is made out of particles

- Matter is moving constantly and randomly

Assumptions of the Kinetic Particle Theory

- Particles are in constant motion and move in random directions

- Particles posses kinetic energy

- Forces of attraction exist between particles

- Heavier particles travel slower than lighter particles

- Particles do not stick to each other after collision (elastic collision)

- Particles do not stick with the walls of container and bounces back of collision with the walls of container

- Particles are small and discrete.

Limitations of the Kinetic Particle Theory

- Forces of attraction between particles are not seen in the model (Only for static picture but can be shown clearly on animation)

- Movement of particles in terms of direction and speed may not be accurately captured on static picture but can be shown clearly on animation

- Distance between particles in model may not be scaled accurately to actual distance between particles

Assumptions and Limitations

- Assumptions are valid statements to set the parameters for the model to work. Without the assumptions, the principles of the model become invalid or irrelevant

- Limitations are features of the model not aligned with the actual properties and not able to illustrate the principals of the phenomenon.