A scientific model is...

• A representation, a prototype of replica of the object/phenomenom that could well explains the physical properties
• It can be represented using animations or static diagrams
• Phenomenon includes physical phenomenom like diffusion, dissolving, boiling, condensation, evaporation, melting, sublimation etc.
• Physical properties includes volume, density, conductivity.

What are some assumations & limitations?

Assumptions

• Assumptions are valid statements to set the parameters for the models to work. Without the assumptions, the principles of the model becomes invalid or irrelevant
• Limitations are features of the model not aligned with the actual properties and not able to illustrate the principles of phenomenon
• Particles are in constant motions and in random directions.
• Particles possess kinetic energy.
• Forces of attraction exist between particles.
• Heavier particles travel slower than lighter particles.
• Particles fo not stick to each other with collision.
• Particles do not stick with the walls of container and bounces back after collision with the walls of the container.
• Particles travel in a straight line.
• Particles are small and discrete.

Limitations

• Forces of attraction between particles are not seen in the model
• Movement of particles in terms of direction and speed may not be accurately captured on static pictire but can be shown clearly on animation
• Distance between particles in model may not be scaled accurately to the actual dstance between particles

During a rock concert:

• Features similar to kinetic particle model

1. During concert, people are closely packed and jumping at fixed positions, just like particles in solid
2. When concert ends, people are moving disorderly sliding past each other but still closly packed, just like in liquid state.

• Assumpations

1. People are large in numbers yet small in size relative to entire concert hall
2. People do not stick to each other upon collision
3. Each person possess kinetic energy
4. Each person moves in a constant and random movement

• Limitations

1. People are of different sizes/ masses unlike particles whidh are of same size and mass of same substance
2. People are not standing in ordered arrangement unlike particles

States (Physical Properties)

Physical Properties

Volume

• Solid: Definite
• Liquid: Definite
• Gas: Indefinite

Shape

• Solid: Definite
• Liquid: Indefinite
• Gas: Indefinite

Density

• Solid: High
• Liquid: Middle
• Gas: Low

Compressibility

• Solid: No
• Liquid: No
• Gas: Yes

Arrangement & motion of particles to explain the physical state:

Solid - The particles of a sold are close together and in a regular pattern. The particles move very little. In solids, the particles are held together by a strong force of attraction.

Liquid - The particles of a liquid are a bit further apart than in a solid and in a less regular pattern. The particles move past each other and keep changing positions as they have more energy than solid partivles thus able to move by rolling and gliding throughout the liquid.

Gas - The particles of a gas is far apart. They have no pattern. The particles can move whenever they can. The particles of a gas are almost free of attraction from each other as they have sufficient energy to overcome forces of attraction completely. 

Kinetic Particle Theory

Physical Change

1. No new substance formed
2. Usually easily reversible
3. May/may not involve heating

Chemical Change

1. New chemical is/are formed
2. Usually irreversible ( only under special conditions )
3. Heat energy may be given off/absorbed
4. Light energy may be given off/absorbed

Signs of a Chemical Change

1. a change in colour
2. production of a gas
3. formation of a precipitate from mixing solutions
4. Change of temperature ( all the above must follow the formation of a new chemical substance ).

Process when new chemical substances are formed

1. reactants -> products 

• New chemical substances formed due to rearrangement of atoms
• No atoms are created/destroyed, according to the Law of Constant Mass

Types of Chemical Reactions

Combination (Synthesis)

• two or more substances combined to form a new substance
• magnesium + oxygen -> magnesium oxide

Decomposition

• substance breaks down 2 or more simpler substances
• calcium carbonate -> calcium oxide + carbon dioxide

Combustion / Burning

• combination of a substance with oxgen
• heat and light energy are given off
• hydrocarbon + oxygen -> carbon dioxide + water

Displacement Reaction

• a chemical reaction with an atom/a group of atoms get replaced by another atom/group of atoms
• hydrogen bromide + chlorine -> hyydrogen chloride + bromine

Definition:
States that all matter is made up of tiny particles and that these particles are in constant random motion.

Assumptions:

• All matter is made up of tiny particles.
• The tiny particles are in constant random motion.
• These particles in motion have kinectic energy.
• Higher the temperature, the faster the movement of these particles.

Melting

• Solid particles gain energy when heated
• particles vibrate faster
• as temperature increases, vibrations also increase
• finally, particles are able to overcome the forces that hold them in their fixed positions