P3 - particle model of matter

What is the particle model of matter?

Matter is made of particles whose arrangement, movement and energy explain its properties.

How are particles arranged in a solid?

Closely packed in a fixed, regular arrangement.

How do particles move in a solid?

They vibrate about fixed positions.

How are particles arranged in a liquid?

Close together but randomly arranged.

How do particles move in a liquid?

They move around each other, allowing the liquid to flow.

How are particles arranged in a gas?

Far apart and randomly arranged.

How do particles move in a gas?

Rapidly and randomly in all directions.

What is density?

Mass per unit volume.

What is the equation for density?

Density = mass / volume; ρ = m / V.

What is the unit of density?

kg/m³ or g/cm³.

What is the unit of mass in the SI system?

Kilograms (kg).

What is the SI unit of volume?

Cubic metres (m³).

How do you convert g/cm³ to kg/m³?

Multiply by 1000.

How do you calculate the volume of a regular solid?

Measure its dimensions and use the appropriate geometric equation.

How do you find the volume of an irregular solid?

Measure the volume of liquid displaced when it is submerged.

How can you find the density of a liquid?

Measure its mass and volume, then divide mass by volume.

What is the aim of the density required practical?

Determine the densities of regular solids, irregular solids and liquids.

How do you measure the mass of a solid in the density practical?

Use a balance.

How do you measure the volume of an irregular solid using displacement?

Record the initial and final liquid levels; subtract to find the displaced volume.

How do you calculate density from practical measurements?

Divide measured mass by measured volume.

Why should you repeat density measurements?

To identify anomalies and calculate a more reliable mean.

What is a change of state?

A physical change between solid, liquid and gas.

What is melting?

Changing from a solid to a liquid.

What is freezing?

Changing from a liquid to a solid.

What is boiling?

Changing from a liquid to a gas throughout the liquid.

What is evaporation?

Particles escape from a liquid's surface to form a gas.

What is condensation?

Changing from a gas to a liquid.

What is sublimation?

Changing directly between a solid and a gas.

What happens to particles during melting?

They gain energy and can move past one another.

What happens to particles during boiling?

They gain enough energy to separate and form a gas.

What happens to particle arrangement during condensation?

Particles become closer together as the gas becomes liquid.

Does the mass change during a change of state?

No, if no matter enters or leaves the system.

Does the temperature change during melting or boiling?

No, it stays constant during the change of state.

Why does temperature remain constant during a change of state?

Energy changes the arrangement and separation of particles rather than their average kinetic energy.

What is internal energy?

The total kinetic and potential energy of all the particles in a system.

What happens to internal energy when a substance is heated?

It increases.

What happens to particle kinetic energy when temperature increases?

Average kinetic energy increases.

What happens to particle potential energy during a change of state?

It changes as particle separation and arrangement change.

What is specific latent heat?

The energy needed to change the state of 1 kg of a substance without changing its temperature.

What is the equation for energy transferred during a change of state?

E = m × L

What do E, m and L represent in E = mL?

E = energy (J); m = mass (kg); L = specific latent heat (J/kg).

What is specific latent heat of fusion?

The energy needed to change 1 kg from solid to liquid without changing temperature.

What is specific latent heat of vaporisation?

The energy needed to change 1 kg from liquid to gas without changing temperature.

Why does vaporisation usually require more energy than melting?

Particles must separate much further against attractive forces.

What is the unit of specific latent heat?

J/kg.

How do you calculate energy needed to melt a mass of substance?

E = mass × specific latent heat of fusion.

How do you calculate energy needed to vaporise a mass of liquid?

E = mass × specific latent heat of vaporisation.

What is the relationship between gas temperature and particle motion?

Higher temperature means greater average kinetic energy.

How do gas particles exert pressure on a container?

They collide with the container walls and exert forces.

What causes gas pressure?

Gas particles colliding with the walls of their container.

What happens to gas pressure if temperature rises at constant volume?

Pressure increases because particles move faster and collide more forcefully and frequently.

Why must volume stay constant when investigating temperature and gas pressure?

To ensure the pressure change is due to temperature rather than a volume change.

What happens to gas pressure if the gas is compressed at constant temperature?

Pressure increases because particles collide with the walls more frequently.

What happens to gas pressure if the volume increases at constant temperature?

Pressure decreases because wall collisions become less frequent.

What is the relationship between pressure and volume for a fixed mass of gas at constant temperature?

Pressure is inversely proportional to volume; p × V = constant.

What happens to gas particle speed when temperature decreases?

Average particle speed decreases.

Why does heating a gas in a sealed, rigid container increase its pressure?

Faster particles collide with the walls more frequently and transfer more momentum.

What is absolute zero?

0 kelvin, the lowest possible temperature.

How do you convert degrees Celsius to kelvin?

K = °C + 273.

Why does a gas exert less pressure when cooled at constant volume?

Particles move more slowly and collide with the walls less forcefully.

What is the difference between boiling and evaporation?

Boiling occurs throughout a liquid at its boiling point; evaporation occurs at the surface at various temperatures.