GCSE AQA Physics - Particle Model of Matter

Density

Mass per unit volume of a substance.

Density =

mass (kg) / volume (m³)

States of matter from highest to lowest density

Solid, liquid, gas

Arrangement of particles in a solid

Particles are held together in a fixed, regular arrangement due to strong forces of attraction.

Energy of particles in a solid

Particles have low energy so can only vibrate about their fixed position.

Arrangement of particles in a liquid

Particles are close together, but can move past each other in an irregular arrangement, due to weaker forces of attraction.

Energy of particles in a liquid

Particles have more energy than solids, so can move in random directions at low speed.

Arrangement and energy of particles in a gas

Particles are spread out and move randomly at high speed, due to almost no forces of attraction between them and high energy.

How can you find the density of a regular solid? (3)

• Use an electric balance to measure it’s mass

• Measure it’s length, width and height to find it’s volume

• Divide mass by volume

How can you find the volume of an irregular solid?

Submerge the solid in a displacement can filled with water, and measure the volume of the displaced water.

How can you find the density of a liquid?

• Place a measuring cylinder on a balance and zero the balance

• Pour 10ml of water into the cylinder and weigh the mass

• Pour another 10ml and repeat the process

• Take an average of the calculated densities

Internal energy

The total kinetic energy and potential energy of all the particles that make up a system.

How does heating change the energy stored within a system?

It increases the energy of particles, either leading to a change in temperature or a change in state.

What type of change is a change of state and why?

• A physical change

• Because the material recovers it’s original properties if the change is reversed

Sublimation

A solid turns straight to a gas

What is energy used for when a substance is melting or boiling instead of raising temperature?

Breaking bonds between particles.

What is energy used for when a substance is condensing or freezing instead of raising temperature?

Forming bonds between particles.

Specific latent heat

The amount of energy needed to change the state of 1kg of a substance without changing it’s temperature.

Specific latent heat of fusion

The specific latent heat for changing between a solid and a liquid.

Specific latent heat of vaporisation

The specific latent heat for changing between a liquid and a gas.

How is the temperature of a gas related to the average energy in the kinetic energy stores of the particles?

The higher the temperature, the higher the average energy.

How do gas particles create pressure in a sealed container? (3)

• Gas particles collide with the walls

• This exerts a force on the walls

• The total force acting over the area of the container causes the gas pressure

Explain the effect of increasing volume on pressure (while keeping temperature constant) (4)

• The spacing between particles increases

• Particles travel a further distance before colliding with the walls of the container

• Collisions per second is reduced

• Pressure decreases

Relationship between pressure and volume

Pressure is inversely proportional to the volume.

pV =

constant

How can a change in pressure cause a change in volume?

If the container can easily change it’s size, any change in the pressure inside or outside will cause the container to compress or expand.

How can doing work mechanically on a gas increase it’s temperature? (3)

• Because we have applied a force to the gas, energy is transferred to the particles

• The internal energy of the gas increases

• This increase the kinetic energy of the particles

• This increases it’s temperature