P6.3. Particle Model of Matter

What is density?

Mass per unit volume.

What is the equation for density?

ρ = m/V.

What is the unit of density?

kg/m³.

What is the unit of mass in the density equation?

kg.

What is the unit of volume in the density equation?

m³.

What does the particle model explain?

The different states of matter and differences in density.

How are particles arranged in a solid?

They are closely packed in a regular arrangement.

How do particles move in a solid?

They vibrate around fixed positions.

How are particles arranged in a liquid?

They are close together but arranged irregularly.

How do particles move in a liquid?

They move around each other.

How are particles arranged in a gas?

They are far apart and arranged randomly.

How do particles move in a gas?

They move rapidly and randomly.

Why are gases much less dense than solids and liquids?

The particles are much further apart.

Why are liquids and solids much denser than gases?

Their particles are much closer together.

What should you be able to do with particle diagrams?

Recognise and draw simple diagrams showing solids, liquids and gases.

What should you be able to explain using particle arrangement?

Differences in density between different states of matter.

What is the required practical for density?

Determine the densities of regular and irregular solid objects and liquids.

How do you find the volume of a regular solid?

Measure its dimensions and calculate its volume.

How do you find the volume of an irregular solid?

Use a displacement technique.

What equipment could be used to measure dimensions in the density practical?

A ruler, micrometer or Vernier callipers, as appropriate.

What happens to mass when a substance changes state?

Mass is conserved.

What happens during melting?

A solid changes into a liquid.

What happens during freezing?

A liquid changes into a solid.

What happens during boiling?

A liquid changes into a gas throughout the liquid.

What happens during evaporation?

A liquid changes into a gas at its surface.

What happens during condensation?

A gas changes into a liquid.

What happens during sublimation?

A solid changes directly into a gas.

What type of change is a change of state?

A physical change.

Why are changes of state physical changes?

The material recovers its original properties when the change is reversed.

What is internal energy?

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

Where is internal energy stored?

In the particles that make up the system.

What happens to internal energy when a system is heated?

The energy stored in the system increases.

What can heating a system do?

It can increase its temperature or cause a change of state.

What does the temperature increase of a substance depend on?

The mass, the type of material and the energy input.

What is specific heat capacity?

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

What is the equation for change in thermal energy?

ΔE = mcΔθ.

What does ΔE represent?

The change in thermal energy, in joules (J).

What does m represent?

Mass, in kilograms (kg).

What does c represent?

Specific heat capacity, in J/kg°C.

What does Δθ represent?

Temperature change, in °C.

What is specific heat capacity measured in?

J/kg°C.

What should you be able to do with the specific heat capacity equation?

Calculate the energy change when the temperature of a material changes.

What is the required practical for specific heat capacity?

Determine the specific heat capacity of one or more materials.

What is latent heat?

The energy needed for a substance to change state.

What happens to the temperature during a change of state?

It stays constant while the change of state occurs.

What happens to the energy supplied during a change of state?

It increases the internal energy of the substance rather than its temperature.

What is specific latent heat?

The energy required to change the state of 1 kg of a substance with no change in temperature.

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

E = mL.

What does E represent?

Energy transferred, in joules (J).

What does m represent?

Mass, in kilograms (kg).

What does L represent?

Specific latent heat, in J/kg.

What is specific latent heat measured in?

J/kg.

What is specific latent heat of fusion?

The energy required to change 1 kg from solid to liquid with no change in temperature.

What is specific latent heat of vaporisation?

The energy required to change 1 kg from liquid to vapour with no change in temperature.

What should you be able to do with the specific latent heat equation?

Calculate the energy change involved in a change of state.

What is the required practical for latent heat?

Measure the latent heat of fusion of water.

What should you be able to interpret?

Heating and cooling graphs that include changes of state.

What is the difference between specific heat capacity and specific latent heat?

Specific heat capacity is energy needed to change temperature; specific latent heat is energy needed to change state without changing temperature.

What happens to the internal energy of a substance when it is heated but does not change state?

Its temperature increases because the particles gain kinetic energy.

What happens to the internal energy during a change of state?

The internal energy increases or decreases while the temperature remains constant.

What is the motion of gas molecules like?

Constant and random.

What is the temperature of a gas related to?

The average kinetic energy of its molecules.

What happens when the temperature of a gas at constant volume increases?

The pressure increases.

What happens when the temperature of a gas at constant volume decreases?

The pressure decreases.

Why does increasing the temperature of a gas increase its pressure at constant volume?

The particles have greater average kinetic energy, so they collide with the container walls more frequently and with greater force.

Why does a gas exert pressure on the walls of its container?

Moving gas particles collide with the walls and exert forces on them.

How is gas pressure related to particle motion?

Greater particle kinetic energy produces more frequent and more forceful collisions with the container walls.

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

The pressure increases.

What should you be able to explain qualitatively about gas temperature and pressure?

At constant volume, increasing temperature increases pressure because the particles have greater average kinetic energy.