## Particulate Nature of Matter

### Changes of state

Solid to liquid: melting
Liquid to gases: evaporation
Liquid to solid: freezing
Gas to liquid: condensing

Solid to gas: sublimation
Gas to solid: sublimation

Note: sublimation is often asked in mcq questions

There is no temperature change while a change of state is occurring

### Kinetic Particle theory

Kinetic theory: Particles behave as hard spheres, constantly moving from place to place (in liquids and gases) and vibrate upon a fixed position (in solids)

• In gases, particles are constantly colliding and changing directions resulting in random movement.
• As temperature increases, particles gain kinetic energy and move faster
• Gases can be compressed easily. Pressure and volume are inversely proportional. This means an increase in pressure at constant temperature results in a decrease in volume.
• Liquids and solids cannot be compressed easily as particles are close together and kinetic theory assumes particles are hard
• Gas in a closed container increases in pressure when it’s heated because the increased kinetic energy moves faster and collide with the walls of the container with greater force

### Explanation of changes of state

• Input of energy is needed to melt and boil a substance
• Energy lessens the force of energy when a substance freezes or condenses
• Energy given out when substance freezes or condenses
• During freezing or condensation particles move slower, losing kinetic energy

### Heating and Cooling Curves

Brownian motion: the random movement of particles in fluids. This happens because they are bombarded by other moving particles in the fluid.

Examples: Random movement of dust particles in still air

Diffusion: spreading movement of one substance into another due to random motion of the particles.

• Overall movement is from higher concentration to lower concentration
• Diffusion is faster in gases as particles move faster.

During change of state, temperature is constant.

• Evidence; Pollen grain were being moved by individual water molecules
• This is how particles are diffused