Particle Model of Matter

What is density?

Mass per unit volume of a substance.

What is the equation for density?

ρ = m / V. Density (kg/m³) = mass (kg) / volume (m³).

What is another common unit for density?

g/cm³.

How do you convert cm³ to m³?

1 m³ = 1,000,000 cm³ - so divide cm³ by 1,000,000.

How are particles arranged in a solid?

Very close together in a regular arrangement - vibrate around fixed positions.

How are particles arranged in a liquid?

Close together but irregular - particles can move past each other.

How are particles arranged in a gas?

Far apart and randomly arranged - move rapidly in random directions.

Why are solids and liquids usually denser than gases?

Their particles are much closer together - more mass in the same volume.

Why can different materials have different densities?

Their particles have different masses and/or different spacing.

RP5 - What does the density practical determine?

Density of regular solid objects, irregular solid objects + liquids.

RP5 - How do you find the density of a regular solid?

Measure mass with balance - measure dimensions - calculate volume - density = mass / volume.

RP5 - How can the volume of a cuboid be calculated?

Volume = length x width x height.

RP5 - What equipment can measure dimensions of a regular solid?

Ruler, Vernier callipers or micrometer - choose appropriate equipment for the size/precision needed.

RP5 - How do you find the density of an irregular solid?

Measure mass - find volume by water displacement - density = mass / volume.

RP5 - How does the displacement method find volume?

Fully submerge object - volume of water displaced = volume of object.

RP5 - How can displacement volume be measured using a measuring cylinder?

Record initial water volume - submerge object - record final volume - object volume = final - initial.

RP5 - How can displacement volume be measured using a Eureka can?

Fill to spout - submerge object - collect displaced water - measure its volume.

RP5 - How do you find the density of a liquid?

Measure mass of empty container - add known volume of liquid - measure total mass - subtract container mass - density = mass / volume.

RP5 - Why should density measurements be repeated?

Identify anomalies + calculate a mean to improve reliability.

What happens to particles when a substance changes state?

Particle arrangement/movement changes - particles themselves do not change.

What are the changes of state between solid and liquid?

Melting - solid to liquid. Freezing - liquid to solid.

What are the changes of state between liquid and gas?

Boiling/evaporating - liquid to gas. Condensing - gas to liquid.

What is sublimation?

Solid changes directly into gas without becoming liquid.

Is mass conserved during a change of state?

Yes - mass stays the same in a closed system.

Are changes of state physical or chemical changes?

Physical - material can recover its original properties if the change is reversed.

What is internal energy?

Total kinetic energy + potential energy of all particles in a system.

What happens to internal energy when a substance is heated?

Energy transferred to the substance increases its internal energy.

What can happen when the internal energy of a substance increases?

Its temperature increases or it changes state.

What does temperature measure in the particle model?

Related to the average kinetic energy of the particles.

What happens to particles when temperature increases without a change of state?

Average kinetic energy increases - particles move/vibrate faster.

What is specific heat capacity?

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

What is the equation for thermal energy change?

ΔE = m x c x Δθ. Energy change (J) = mass (kg) x specific heat capacity (J/kg°C) x temperature change (°C).

What does a high specific heat capacity mean?

More energy is needed to produce the same temperature increase.

What happens to temperature during a change of state?

Temperature stays constant while the state is changing.

Why does temperature stay constant during a change of state?

Energy changes the potential energy/arrangement of particles rather than increasing their kinetic energy.

What is latent heat?

Energy needed for a substance to change state without changing temperature.

What is specific latent heat?

Energy required to change the state of 1 kg of a substance with no temperature change.

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

E = m x L. Energy (J) = mass (kg) x specific latent heat (J/kg).

What is the unit of specific latent heat?

J/kg.

What is specific latent heat of fusion?

Energy required to change 1 kg from solid to liquid without changing temperature.

What is specific latent heat of vaporisation?

Energy required to change 1 kg from liquid to gas without changing temperature.

What does a sloping section on a heating graph represent?

Temperature increasing - particle kinetic energy increases.

What does a flat section on a heating graph represent?

Change of state - temperature stays constant while particle potential energy increases.

What does a flat section on a cooling graph represent?

Change of state - temperature stays constant while internal energy decreases.

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

SHC changes temperature without changing state - SLH changes state without changing temperature.

Why is specific latent heat of vaporisation usually greater than fusion?

More energy is needed to separate particles much further apart into a gas.

How do gas particles move?

Constant rapid random motion.

What causes gas pressure?

Gas particles collide with container walls - collisions exert forces on the walls.

Why does a gas exert pressure in all directions?

Particles move randomly and collide with all surfaces of the container.

How is gas temperature related to particle motion?

Higher temperature - greater average kinetic energy - particles move faster.

What happens to gas pressure when temperature increases at constant volume?

Pressure increases.

Why does gas pressure increase when temperature increases at constant volume?

Particles move faster - collide with walls more frequently + with greater force.

What happens to gas pressure when temperature decreases at constant volume?

Pressure decreases.

What can happen to the volume of a gas when pressure changes?

Gas can be compressed or expanded. (Physics only)

In what direction does gas pressure exert a force on a surface?

At right angles to the surface. (Physics only)

What happens when work is done on a gas by compressing it?

Energy is transferred to the gas - internal energy increases - temperature can increase. (Physics only)

Give an everyday example of compression heating a gas.

A bicycle pump can become warm when air is compressed. (Physics only)

What happens to gas pressure when volume decreases at constant temperature?

Pressure increases. (HT Physics only)

Why does decreasing gas volume increase pressure at constant temperature?

Particles have less space - collide with container walls more frequently. (HT Physics only)

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

Pressure is inversely proportional to volume. (HT Physics only)

What equation links pressure and volume for a fixed mass of gas at constant temperature?

p x V = constant, so p1 x V1 = p2 x V2. (HT Physics only)

What does inverse proportionality between pressure and volume mean?

If volume halves, pressure doubles - if volume doubles, pressure halves. (HT Physics only)

How do you calculate a new gas pressure or volume?

Use p1 x V1 = p2 x V2 - keep volume units consistent. (HT Physics only)