This topic uses the particle model to explain properties of solids, liquids, and gases — density, pressure, changes of state, specific heat capacity, latent heat, and gas laws.
Solids: particles vibrate in fixed positions, strong forces, definite shape/volume. Liquids: particles move past each other, weaker forces, definite volume but not shape. Gases: particles move freely, negligible forces, fill container. Density ρ = m/V (kg/m³). Measure: regular shape → calculate volume; irregular → displacement method. Changes of state: melting, boiling, evaporation, condensation, sublimation. During change of state: temperature stays constant (energy used to break/form bonds, not increase KE).
Specific heat capacity: E = mcΔθ (energy = mass × SHC × temperature change). Latent heat: E = mL (energy for change of state at constant temperature). Specific latent heat of fusion (solid↔liquid) and vaporisation (liquid↔gas). Pressure P = F/A (Pa). Liquid pressure P = ρgh (increases with depth and density). Gas pressure: caused by particles colliding with walls. Boyle\'s law: P₁V₁ = P₂V₂ (at constant temperature). Pressure and temperature: at constant volume, P ∝ T (in kelvin). T(K) = T(°C) + 273.
During a change of state (e.g., melting or boiling), the energy supplied is used to break intermolecular bonds rather than increase the kinetic energy of particles. Temperature is a measure of the average kinetic energy of particles — so if kinetic energy isn\'t increasing, the temperature doesn\'t rise. All the energy goes into overcoming the attractive forces between particles. Once all bonds are broken (change of state complete), the temperature starts rising again. The energy needed per kilogram is called the specific latent heat (L), and the total energy is E = mL.
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