topic 3 - particle model of matter

What are the three states of matter?

Solid, liquid and gas.

How are particles arranged in a solid?

Particles are closely packed in a regular arrangement and vibrate about fixed positions.

How are particles arranged in a liquid?

Particles are close together in an irregular arrangement and can move past each other.

How are particles arranged in a gas?

Particles are far apart, randomly arranged and move rapidly in random directions.

How do the particles move in a solid?

They vibrate about fixed positions.

How do the particles move in a liquid?

They move randomly and slide past one another.

How do the particles move in a gas?

They move rapidly and randomly in all directions.

Why are solids difficult to compress?

Their particles are already close together, with very little space between them.

Why are gases easy to compress?

Gas particles are far apart, so the spaces between them can be reduced.

Why can liquids flow but solids cannot?

Liquid particles can move past one another, while solid particles vibrate about fixed positions.

What is density?

Mass per unit volume.

What is the equation for density?

Density = mass ÷ volume; ρ = m ÷ V.

What does each symbol mean in ρ = m ÷ V?

ρ = density in kg/m³, m = mass in kg, V = volume in m³.

What is the rearranged equation for mass?

m = ρ × V.

What is the rearranged equation for volume?

V = m ÷ ρ.

How can you find the volume of a regular solid?

Measure its dimensions and use the appropriate geometric equation, such as length × width × height for a cuboid.

How can you find the volume of an irregular solid?

Use water displacement: measure the volume of water displaced when the object is fully submerged.

How can you find the volume of a liquid?

Measure it using a measuring cylinder or another suitable measuring instrument.

How can you find the density of an irregular solid experimentally?

Measure its mass using a balance, find its volume by water displacement, then calculate density = mass ÷ volume.

What happens to particles when a substance melts?

Energy is transferred to the substance, allowing particles to overcome some of the forces holding them in fixed positions.

What is melting?

The change of state from solid to liquid.

What is freezing?

The change of state from liquid to solid.

What is boiling?

The change of state from liquid to gas throughout the liquid at its boiling point.

What is evaporation?

The change of state from liquid to gas at the surface, which can occur below the boiling point.

What is condensation?

The change of state from gas to liquid.

What is sublimation?

The change of state directly from solid to gas, without becoming liquid first.

What is deposition in changes of state?

The change of state directly from gas to solid.

What is the difference between boiling and evaporation?

Boiling occurs throughout the liquid at its boiling point; evaporation occurs at the surface and can happen below the boiling point.

What happens to temperature during melting or boiling of a pure substance?

Temperature stays constant during the change of state because energy is used to change the substance's state rather than increase its temperature.

What happens to particles during a change of state?

The particles themselves do not change; their arrangement, separation and energy change.

What is internal energy?

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

What happens to internal energy when a substance is heated?

Its internal energy increases.

How can internal energy increase?

Particles can gain kinetic energy, increasing temperature, or gain potential energy as their separation changes during a change of state.

What is the difference between temperature and internal energy?

Temperature relates to the average kinetic energy of particles; internal energy is the total kinetic and potential energy of all particles.

What happens to particle kinetic energy when temperature increases?

The average kinetic energy of the particles increases.

Why does temperature remain constant while a pure substance changes state?

The energy transferred changes the potential energy associated with particle separation rather than increasing average kinetic energy.

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 energy transferred by heating?

ΔE = m × c × Δθ.

What does each symbol mean in ΔE = mcΔθ?

ΔE = energy transferred in J, m = mass in kg, c = specific heat capacity in J/kg°C, Δθ = temperature change in °C.

How do you calculate specific heat capacity?

c = ΔE ÷ (m × Δθ).

What factors determine the energy needed to raise a substance's temperature?

Its mass, specific heat capacity and temperature change.

What does a substance with a high specific heat capacity require?

More energy to raise the temperature of each kilogram by 1°C.

What is the specific heat capacity required practical?

Measure the mass of a block, insert an electric heater and thermometer, insulate the block, record the initial temperature, heat for a measured time and record the final temperature.

How can the energy supplied to an electric heater be calculated?

E = V × I × t, where V is potential difference, I is current and t is time.

How do you calculate specific heat capacity in the practical?

Calculate energy supplied using E = VIt, measure the mass and temperature change, then use c = E ÷ (m × Δθ).

Why is insulation used in the specific heat capacity practical?

To reduce energy transferred to the surroundings.

Why should the heater be in good thermal contact with the block?

To transfer energy efficiently into the block.

What are sources of error in the specific heat capacity practical?

Energy lost to the surroundings, energy heating the apparatus, and inaccuracies in mass, temperature, current, voltage or time measurements.

How can the specific heat capacity practical be improved?

Use insulation and a lid where appropriate, ensure good thermal contact, measure accurately and repeat readings.

What is specific latent heat?

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

What is specific latent heat of fusion?

The energy required to change 1 kg of a substance from solid to liquid at its melting point without changing temperature.

What is specific latent heat of vaporisation?

The energy required to change 1 kg of a substance from liquid to gas at its boiling point without changing temperature.

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

E = m × L.

What does each symbol mean in E = mL?

E = energy transferred in J, m = mass in kg, L = specific latent heat in J/kg.

How do you calculate specific latent heat?

L = E ÷ m.

Why does temperature not change during a change of state even though energy is supplied?

The energy changes the potential energy of the particles by overcoming forces between them, rather than increasing their average kinetic energy.

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

More energy is generally needed to separate particles into a gas than to loosen them enough to form a liquid.

What happens to internal energy during melting?

Internal energy increases because energy is transferred to overcome some of the forces between particles, while temperature remains constant.

What happens to internal energy during boiling?

Internal energy increases because energy is used to separate particles further, while temperature remains constant.

What is gas pressure caused by?

Gas particles colliding with the walls of their container and exerting forces on them.

How do gas particles produce pressure?

Their collisions with the container walls exert a force; pressure is force per unit area.

What is the equation for pressure?

p = F ÷ A.

What do the symbols mean in p = F ÷ A?

p = pressure in pascals (Pa), F = force in newtons (N), A = area in m².

What is the equation for force from pressure?

F = p × A.

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

Pressure increases because particles move faster and collide with the walls more frequently and with greater force.

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

Pressure increases because particles collide with the walls more frequently.

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

Pressure decreases because particles collide with the walls less frequently.

How does heating a gas affect the particles' kinetic energy?

It increases their average kinetic energy, so they move faster.

What happens to the volume of a gas when it is heated at constant pressure?

The gas expands because the particles move faster and the volume increases to keep pressure constant.

What is absolute zero?

0 K, equivalent to approximately −273°C; the lowest possible temperature.

How do you convert degrees Celsius to kelvin?

Temperature in K = temperature in °C + 273.

How do you convert kelvin to degrees Celsius?

Temperature in °C = temperature in K − 273.

What is the relationship between the kelvin temperature and the average kinetic energy of gas particles?

For an ideal gas, average kinetic energy is directly proportional to absolute temperature in kelvin.

What is Brownian motion?

Random movement of visible particles caused by collisions with much smaller, rapidly moving particles in a fluid.

How does Brownian motion provide evidence for particles?

It shows that tiny particles in fluids are constantly moving and colliding with larger visible particles.

What is the difference between mass and weight?

Mass is the amount of matter in an object, measured in kg; weight is the force due to gravity, measured in N.

How should you answer a density calculation question?

Write density = mass ÷ volume, convert quantities into consistent units, substitute the values and give the answer with the correct unit.

What are common units for density?

kg/m³ or g/cm³; ensure mass and volume units match the density unit.

How do you convert g/cm³ to kg/m³?

Multiply by 1,000.

What should you remember about energy calculations in this topic?

Use ΔE = mcΔθ for temperature changes and E = mL for changes of state; use the correct units and rearrange when needed.