Particle Model and Pressure
States of Matter
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Particle arrangement | Regular lattice | Close but random | Far apart, random |
| Particle motion | Vibrate about fixed positions | Move/flow past each other | Move rapidly in all directions |
| Density | High | High (similar to solid) | Very low |
| Shape | Fixed | Takes container shape | Fills container |
| Volume | Fixed | Fixed | Fills container |
Density
Density (ρ) = mass ÷ volume: ρ = m/V (kg/m³)
Core Practical 8 — Measuring density:
- Regular solid: measure mass with balance; calculate volume using formula (e.g. V = l × w × h for cuboid; V = 4/3πr³ for sphere).
- Irregular solid: use a displacement can/Eureka can — volume of water displaced = volume of solid.
- Liquid: measure mass of known volume (e.g. using measuring cylinder and balance).
Internal Energy and Changes of State
Internal energy is the total kinetic and potential energy of all particles in a substance.
Heating increases internal energy:
- If no change of state: KE increases → temperature rises.
- During a change of state (e.g. melting or boiling): potential energy increases (particles separate), temperature stays constant (flat region on heating curve).
Specific latent heat (L): energy needed to change the state of 1 kg of a substance without temperature change.
E = mL (joules; m in kg; L in J/kg)
- Latent heat of fusion (melting/solidifying)
- Latent heat of vaporisation (boiling/condensing)
Gas Pressure and Kinetic Theory
Gas pressure is caused by gas molecules colliding with the walls of their container. Each collision exerts a force on the wall; billions of collisions per second create a measurable pressure.
Boyle's Law (constant temperature): pressure and volume are inversely proportional.
p₁V₁ = p₂V₂
Increasing pressure:
- Decrease volume (compress gas): molecules hit walls more frequently → higher pressure.
- Increase temperature at constant volume: molecules move faster → hit walls harder and more frequently → higher pressure.
Absolute zero: at −273°C (0 K), molecules have minimum kinetic energy. The Kelvin temperature scale starts here.
Temperature conversion: T (K) = T (°C) + 273
Pressure Law (constant volume): p/T = constant (T in Kelvin): p₁/T₁ = p₂/T₂
Core Practical 8 — Investigating relationship between pressure and volume
Equipment: sealed gas syringe or Boyle's Law apparatus, pressure gauge.
Method:
- Record the initial volume of trapped gas at atmospheric pressure.
- Compress the gas (reduce volume) and record pressure at each step.
- Plot a graph of p vs 1/V — should be a straight line through origin confirming p ∝ 1/V.
- Or plot p vs V — should be a hyperbola; calculate pV at each point — should be constant.
AI-generated · claude-opus-4-7 · v3-edexcel-physics