# Particle Model of Matter topic 3

• Particle Model of Matter
• Density of Materials
• Solids: strong forces of attraction hold the particles together in a fixed, regular arrangement. The particles don't have much energy so they can only vibrate about their fixed positions. The density is generally highest in this state as the particles are close together.
• Liquids: there are weaker forces of attraction between particles. The particles are close together but can move past each other and form irregular arrangements They have more energy than particles in a solid and move in random directions at low speeds. Liquids are generally less dense than solids.
• Gases: there are almost no forces of attraction between particles. Particles have more energy and are free to move and travel at high speeds in random directions. They have low densities.
• Density=  Mass/volume
• Internal Energy and Changes of state
• internal energy is the energy stored by the particles that make up a system. Heating the system transfers energy to its particles, increasing the internal energy. A change in state occurs if the substance is heated enough- the particles will have enough energy to break the bonds holding them together.
• A change of state conserves mass. The changes of state are:
• Freezing
• Melting
• Boiling/ evaporating
• Condensing
• Sublimating
• Depostion
• Specific Latent Heat (SLH)
• specific latent heat is the energy needed to change the state of 1kg of a substance.
• Specific latent heat of fusion= the SLH for melting or freezing.
• Specific latent heat of vaporisation= the SLH for evaporating/ boiling or condensing
• Energy= Mass x SLH
• Particle Motion in Gases
• Average energy in kinetic stores is related to temperature. The higher the temperature the higher the average energy. So if you increase the temperature of a gas, the average speed of its particles increases.
• Colliding gas particles create pressure. A change in pressure can cause a change in volume.
• Doing work on a gas can increase its temperature. You can do work on a gas mechanically eg with a bike pump. The gas applies pressure to the plunger of the pump. This transfers energy to the kinetic energy stores of the gas particles, increasing the temperature. If the pump is connected to the tyre you should feel it getting warmer.