AQA GCSE Physics P6 Molecules and matter SEPARATE

State the equation that links mass, volume and density

mass = density x volume (my dense vulture)

What are the units of density?

kg/m³

What are the units of volume?

m³

What are the units of mass?

kg

Describe the arrangement and motion of particles in a solid

particles are close together, in a regular pattern, in fixed positions, vibrating

Describe the arrangement and motion of particles in a liquid

particles are close together, in a random arrangement, can move around

Describe the arrangement and motion of particles in a gas

particles are far apart, moving in all directions, move fast with a range of speeds

Use kinetic theory to explain why solids have a fixed shape

Because particles are in fixed positions and have strong forces of attraction between them (holding them together strongly)

Use kinetic theory to explain why gases will fill the entire container.

Because particles move in all directions at fast speeds with negligible forces of attraction between them.

Use kinetic theory to explain why gases are easy to compress

Because particles are far apart with large spaces between them (so can be pushed much closer together)

Describe the density of a solid or liquid

High density (large mass per unit volume)
Particles are close together.

Describe the density of a gas

Low density (small mass per unit volume).
Particles are far apart.

Density required practical (method, equipment, calculation)

Measure mass in kg using a balance.
Measure volume using a ruler (dimensions of a regular solid V=wxlxh) or a measuring cylinder (liquids) or a displacement (Eureka) can with water level with spout, add irregular solid so V=volume of water displaced into a measuring cylinder.
Use the equation: density=mass/volume

Mass is conserved when substances change state because...

no particles are gained or lost, they are just arranged differently.

What happens when a solid melts?

Solid changes into liquid.
Internal energy increases.
Potential energy of the particles increase as bonds break.
Temperature remains constant as average kinetic energy of the particles stays constant.

What happens when a liquid boils?

Liquid changes into gas.
Internal energy increases.
Potential energy of the particles increase as bonds break and particles move far apart.
Temperature remains constant as average kinetic energy of the particles stays constant.

What happens when a liquid evaporates?

liquid changes into gas (can be below boiling point - eg a puddle on a cool day)

What happens when a gas condenses?

Gas changes to a liquid.
Internal energy decreases.
Potential energy of the particles decreases as stronger bonds are formed and particles get closer together.
Temperature remains constant as average kinetic energy of the particles stays constant.

Explain what happens when a liquid freezes

Liquid changes into a solid
Internal energy decreases.
Potential energy of the particles decreases as stronger bonds are formed.
Temperature remains constant as average kinetic energy of the particles stays constant.

What is subliming?

Change of state from solid to gas.
(not in the Physics course)

What are physical changes?

Changes of state are physical changes because the material recovers its original properties if the change is reversed.
For example, changes of state.

What is internal energy?

The total energy stored inside a system by its particles.
Internal energy =total k.e. + total p.e.
(of all the particles)

When does internal kinetic energy increase?

When the temperature of a substance increases (sloped part of graph)

When does internal potential energy increase?

When the particles move apart, mainly during a change of state (horizontal part of graph).
No effect on temperature.

What happens to the temperature and internal energy of a substance as it is changing state?

Temperature stays constant.
Internal energy increases due to increase in potential energy of particles.
(it is still being heated but the heat energy breaks bonds between particles and moves them further apart instead of raising the temperature)

State 2 things that can happen when a substance is heated.

1. Temperature rise
2. Change of state
(NOT both at the same time)

State the units of temperature

°C

State the units of energy (change)

Joules (J)

Define Specific Heat Capacity

The energy needed to raise the temperature of 1kg of a substance by 1°C

Define Specific Latent Heat

The energy needed to change the state of 1kg of a substance at constant temperature

What is fusion?

It means melting

What is vaporisation?

It means boiling

What are the units of specific latent heat?

J/kg

What is the temperature of a gas directly proportional to?

The average kinetic energy of its particles

(when an object is heated, it's particles gain k.e. and move faster)

Explain the effect of temperature change on gas pressure

If temperature of a gas is increased, the pressure increases (if the volume remains constant) because the particles have more kinetic energy so move faster and collide with the walls of the container more often and with more force.

What causes gas pressure?

Gas molecules colliding with the walls of the container, exerting a force.

Why does ice melt?

Because the internal energy of the ice increases when energy is transferred from the surroundings to the ice.
(due to the temperature difference)

Explain why thermal energy moves from place to place

Because of temperature differences, energy flows from warmer places to cooler places

Why do substances have different melting points?

They have different strength of bonds between particles so different amounts of energy needed to break the bonds

State 2 ways to make a gas condense

1. lower the temperature
2. increase the pressure (particles move closer together)

Which direction is the force produced by gas pressure?

At right angles to the walls of the container or surface

Explain the effect of changing volume on pressure (at constant temperature)

When the volume of the gas decreases, pressure increases.
Pressure is inversely proportional to volume because...
- in a smaller volume, the number of collisions each second between the gas molecules and the walls of the container increases
- so the force on the inside surfaces increases
- so the pressure increases

How is work done on a gas?

A force is exerted on it to reduce its volume

What is the effect of doing work on a gas?
(for example, using a force to compress it)

The internal energy of the gas increases which can cause the temperature to increase.

Why does the internal energy of air increase as a bicycle tyre is inflated?

Work is done on the air so the average kinetic energy of the particles increases so the temperature of the air increases.

Explain how to prove that the pressure is inversely proportional to the volume of a gas?

Show that p x V equals a constant value.
Take 3 sets of values from a line graph or data table.