# P3 - Particle Model of Matter

?
• Created by: Benny52
• Created on: 02-03-19 11:37

## The Particle Model & Motion in Gases

• Solids - strong forces of attraction hold particles close together in fixed, regular arrangement. Don't have much energy - can only vibrate.
• Liquids - weaker forces of attraction between particles. Close together, but can move past each other, & form irreguar arrangements. More energy than particles in solid - move in random directions at low speeds.
• Gases - almost no forces of attraction between particles. More energy than in particles of liquids & solids. Free to move & constantly moving with random directions & speeds.
• Particles in gases collide with each other & anything else in the way. When they collide with something, they exert force on it. Pressure - force exerted per unit area. Sealed container - outward gas pressure is total force force exerted by all particels in gas on unit area of container walls.
• Increase gas temp. - energy transferred to kinetic energy stores of particles.  Higher temp. - higher average energy - average speed of particles increase - energy in particles' kinetic energy stores is 1/2mv(squared). For gas at constant volume, increasing temp. increases pressure - particles moving quicker - sides of container hit more often. Each particle has larger momentum - exert larger force when colliding - increases total force excreted on unit area & increases pressure.
1 of 4

## Density of Materials

• Density - measure of 'compactness' of substance. Relates to mass of substance to how much space it takes up. Units = kg/m(cubed) or g/cm(cubed).
• Density = Mass / Volume               P = m / V
• Dense material - particles packed tightly together. Less dense material - particles more spread out - compress material & particles would move closer together - more dense. Solids denser than liquids & liquids denser than gases.

SEE PRACTICAL SHEET FOR PRACTICAL

2 of 4

## Internal Energy & Changes of State

• Particles in system have energy in kinetic, & potential energy stores - due to their positions. Internal energy of system - total energy particles have in potential & kinetic energy stores. Heating system transfers energy to particles, increasing internal energy - leads to change in temp. or state. If temp. changes, size of change depends on mass of substance, its specific heat capacity & the energy input. Change in state - if object is heated enough for particles to have enough energy in kinetic energy stores to break bonds holding them together.
• State can also change due to cooling - particles lose energy & form bonds.
• Solid - liquid = melting. Liquid - gas = boiling/evaporation. Gas - liquid = condensing. Liquid - solid = freezing. Solid - gas = sublimating.
• Change of state = physical change - don't end up with new substance. No. of particles dont change - arranged differently - mass conserved.
3 of 4

## Specific Latent Heat

• When substance melting or boiling, energy put it so internal energy increases, but energy used for breaking intermolecular bonds, not raising temp. Flat spots on heating graph - energy transferred by heating but not used to change temp.
• When substance condensing or freezing, bonds forming between particles releases energy - internal energy decreases but temp. doesn't decrease until change of state is over.
• Specific latent heat = amount of energy needed to change 1kg of substance from one state to another without changing temp. For cooling, its the energy released by change of state. Changing between solid & liquid - specific latent heat of fusion. Liquid & gas - specific latent heat of vapourisation.
• Energy = Mass x Specific Latent Heat          E = mL     Specifc Latent Heat = J/kg
4 of 4