GCSE / Physics
Particle Model of Matter
Revise the GCSE Physics particle model of matter, including density, states of matter, changes of state, internal energy, specific heat capacity, specific latent heat, heating and cooling curves, particle motion in gases, gas pressure and pressure-volume relationships.
The particle model of matter explains the behaviour and properties of solids, liquids and gases by considering how particles are arranged, how they move and how much energy they have.
Density in physics describes how much mass is contained in a given volume and is calculated using , where is density, is mass and is volume.
Solids usually have a high density because their particles are packed closely together in fixed positions, while gases usually have a much lower density because their particles are far apart.
The density of a regular solid can be found by measuring its mass and calculating its volume from its dimensions, while the density of an irregular solid can be found using a water displacement method.
Changes of state include melting, freezing, boiling, evaporation, condensation and sublimation, and these are physical changes because no new substance is formed.
Mass is conserved during changes of state, so the total mass before and after melting, freezing, boiling or condensing remains the same in a closed system.
Internal energy is the total kinetic energy and potential energy of all the particles in a system, and heating increases the energy stored by the particles.
Temperature is linked to the average kinetic energy of particles, so heating generally makes particles move faster unless the substance is undergoing a change of state.
The change in thermal energy of a substance can be calculated using , where is mass, is specific heat capacity and is the temperature change.
Specific heat capacity is the amount of energy needed to raise the temperature of 1 kg of a substance by 1°C, so materials with a high specific heat capacity require more energy to heat up.
During a change of state, energy is transferred without a change in temperature because the energy changes the potential energy of the particles rather than their average kinetic energy.
The energy transferred during a change of state is calculated using , where is mass and is the specific latent heat of the substance.
Specific latent heat of fusion refers to energy transferred during a solid–liquid change, while specific latent heat of vaporisation refers to energy transferred during a liquid–gas change.
Heating and cooling curves show how temperature changes as energy is transferred, with flat sections representing changes of state and sloping sections representing temperature changes within one state.
Gas particles move continuously and randomly, and gas pressure is caused by collisions between these particles and the walls of their container.
At constant volume, increasing the temperature of a gas increases its pressure because the particles move faster and collide with the container walls more frequently and with greater force.
For a fixed mass of gas at constant temperature, pressure and volume are inversely related and can be calculated using or .
Reducing the volume of a gas increases its pressure because the particles have less space to move and collide with the container walls more often.
Gases are much easier to compress than solids and liquids because there is a large amount of empty space between gas particles.
Doing work on a gas transfers energy to it, increasing its internal energy and often raising its temperature, as can happen when air is compressed in a bicycle pump.