GCSE Physics P3: Particle Model of Matter

density (2)

- mass per unit volume

density = mass/volume

solids, liquids and gases

- solids and liquids have similar densities as the space between particles however liquids have a lower density than solids

- gases have far lower density as the spacing between atoms increase x10 as particels have a lot of energy to move, so volume increases greatly so density decreases molecules in a gas are in constant random position

change of state

- mass is conserved

- physical changes are revsersible but not chemical changes as the materia retains its original properties when reversed

solid to gas

gas to solid

sublimation (dry ice/solid co2)

desublimation

initial energy

sum of kinetic and potential energies of all the particles in a system

specific heat capacity

amount of energy required to raise the temperature of 1kg of substance by 1 degrees celsius

change in thermal energy equation

mass x specific heat capacity x temp change

Specific Latent Heat of Fusion

The energy required to change the state of 1 kg of a substance from solid to liquid at a constant temperature.

It is released during freezing and taken in when melting

Specific Latent Heat of Vaporisation

The energy required to change the state of 1 kg of a substance from liquid to gas at a constant temperature.

It is released during condensation and taken in during boiling

energy for a change of state equation

mas x specific latent heat

graph showing temp of ice (6)

- At A it is a solid

- At B reaches 0 degrees

- From B to C there is no temp change because the energy is used through melting

- From C to D it is in a liquid state

- From D to E the water is boiling and it takes longer because evaporation takes more energy

- From E to F the gas is heating

Pressure in a gas

Gas particles collide with the walls of the container

Each collision exerts a force

The force is at right angles to the surface

The pressure is the total force applied over the area of the container in a given time

P=F/A

Pressure in a gas, increasing the temperature

Increasing the temperature increases the speed of gas molecules

There are more frequent collisions with the walls of the container

Each collision exerts a larger force

The total force across the area of the container in a given time increases

So the pressure increases

Pressure in a gas, decreasing the volume TEMPERATURE CONSTANT

There are more frequent collisions with the walls of the container

The total force across the area of the container in a given time increases

So the pressure increases;

work done equation

work done = force x distance = force/area x (area x distance) = pressure x volume

Model Answer: Work done on a gas TEMPERATURE CHANGES

Work is done on the gas when decreasing its volume.

This increases the internal energy of a gas

And so the temperature increases.

(the opposite is true if the volume increases)

Boyle's Law

Pressure and volume in a gas are inversely proportional at a constant temperature;

Pressure and volume in a gas are inversely proportional at a constant temperature;

- the particles collide with the wall which is moving inward

- so the particles gain momentum as the rebound velocity is greater than the approaching velocity

- so as the particle has a greater velocity