P3 - Particle Model of Matter

Describe the arrangement of particles in solids, liquids, and gases.

Solid – fixed, close; Liquid – close but move past; Gas – far apart, random

State the equation for density.

p = m / V

What is internal energy?

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

What happens to internal energy when a substance is heated?

Particles gain kinetic energy and move faster.

During a change of state, what happens to temperature?

It stays constant while bonds are broken or formed.

State the equation for specific latent heat.

E = mL

What is the difference between specific latent heat of fusion and vaporisation?

Fusion – solid to liquid; Vaporisation – liquid to gas.

Required Practical: Measuring density.

Measure mass with a balance; find volume (e.g. displacement for irregular solids); use

p = m / V

How does pressure in a gas relate to temperature?

Increasing temperature increases pressure (particles move faster and collide more often).

Why do gases have much lower densities than solids and liquids?

Gas particles are far apart with large spaces between them, so the mass per unit volume is much lower.

Describe how heating a solid causes it to melt in terms of energy stores.

Heating increases internal energy — particles vibrate faster, weakening forces between them until they can move freely (change of state)

What happens to the average kinetic energy of particles when temperature doubles (in Kelvin)?

It doubles, because average kinetic energy is proportional to absolute temperature (in K).

State the equation to calculate pressure from a force on an area.

p = F / A

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

Particles collide with the walls, exerting a force per unit area due to changes in momentum.

What does a flat section on a heating curve represent?

A change of state — energy is used to break or form bonds, not increase temperature.

Why does the temperature remain constant during melting or boiling?

Energy goes into potential energy (separating particles), not kinetic energy.

Why does water have a higher specific latent heat than ethanol?

Hydrogen bonds between water molecules require more energy to break.

Give one industrial use of specific latent heat.

In refrigeration — evaporation of a liquid coolant absorbs energy (latent heat), cooling the surroundings.

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

Pressure increases because particles move faster, collide more often and with greater force

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

Volume decreases — Boyle’s Law:

p1 X V1 = p2 X V2

State the relationship between pressure and volume for a fixed mass of gas at constant temperature.

Pressure is inversely proportional to volume.

Why should temperature in gas laws always be measured in Kelvin?

Because particle kinetic energy is directly proportional to absolute temperature, not °C.

Explain why a gas can do work when it expands.

The gas exerts a force over a distance on the surroundings — transferring energy.

Required Practical: Describe how to determine the density of an irregular solid.

Measure mass on a balance; measure displaced water volume using a eureka can; calculate p = m / V

Explain in terms of energy why compressing a gas quickly can make it hot.

Work is done on the gas, increasing internal energy and therefore temperature.

Why is the internal energy of a gas zero at absolute zero (0 K)?

Particles have no kinetic energy, so total internal energy = 0 J.

How does gas pressure relate to Newton’s third law?
A:

Particles exert a force on container walls; walls exert an equal and opposite force back on the gas.

Explain why evaporation causes cooling.

Fastest particles escape from the liquid’s surface, reducing average kinetic energy and therefore temperature of the remaining liquid.

How does increasing the number of particles affect gas pressure if temperature and volume remain constant?

Pressure increases — more particles → more collisions per second.

What type of relationship is there between internal energy and temperature?

Directly proportional, as higher temperature means higher average kinetic energy of particles

Q: In a sealed container, what happens to pressure if both temperature and number of particles double?

Pressure quadruples, since both higher temperature and particle number increase collision frequency and energy.