AQA GCSE Physics (8463) · Paper 1
🌡️ Particle Model of Matter
Revision notes written to the specification, with examiner tips and the required practicals. Every point here has flashcards in the Stickwise app.
Density & states
Solids are the densest state because their particles are packed closest together, while gases are around 1000 times less dense, because the same particles are spread far apart with mostly empty space between them. When a substance changes state, mass is conserved and the particles themselves do not change; only their arrangement and energy are different, which is why a change of state can always be reversed.
Internal energy & latent heat
Internal energy is the total kinetic energy and potential energy of all the particles in a system. Heating a system increases its internal energy, either by raising its temperature, which speeds up the particles, or by changing its state, which breaks the bonds between particles.
The graph stays flat during melting and boiling because all the incoming energy is being used to break the bonds between particles, raising their potential energy, rather than speeding the particles up. This means the temperature stays constant until the change of state is complete, and this hidden energy is called the latent heat.
Gas pressure
Gas particles collide with the walls of their container billions of times a second, and each collision produces a tiny force; together, these collisions create pressure. Heating a gas at a fixed volume makes its particles move faster, so they hit the walls more often and with more force, and the pressure rises. The average kinetic energy of the particles increases with temperature.
(Triple) For a fixed mass of gas at constant temperature, pressure × volume = constant. If the volume is squashed to half, the pressure doubles, because the same particles now hit the walls twice as often; pressure and volume are inversely proportional.