# OCR - P6: Matter – models and explanations

 P6.2 How does the particle model explain the effects of heating? Background to the topic What you should be able to do: The particle model of matter describes the arrangements and behaviours of particles (atoms and molecules); it can be used to predict and explain the differences in properties between solids, liquids and gases. In this model: All matter is made of very tiny particles. There is no other matter except these particles (in particular, no matter between them). Particles of any given substance are all the same. Particles of different substances have different masses. There are attractive forces between particles. These differ in strength from one substance to another. In the solid state, the particles are close together and unable to move away from their neighbours. In the liquid state, the particles are also close together, but can slide past each other. In the gas state, the particles are further apart, and can move freely. The particle model is an example of how scientists use models as tools for explaining observed phenomena. The particle model can be used to describe and predict physical changes when matter is heated. The particles are always moving: in the solid state, they are vibrating; in the liquid state, they are vibrating and jostling around; in the gas state, they are moving freely in random directions. A substance in the gas state exerts pressure on its container because the momentum of the particles changes when they collide with walls of the container. The hotter something is, the higher its temperature is and the faster its particles are vibrating or moving. Careful experimentation and mathematical analysis showed that the temperature of a substance was linked to the kinetic energy of its atoms or molecules. 1. Explain the differences in density between the different states of matter in terms of the arrangements of the atoms or molecules You should be able to use the particle model to explain familiar or unfamiliar phenomena and make predictions. 2. Use the particle model of matter to describe how mass is conserved, when substances melt, freeze, evaporate, condense or sublimate, but that these physical changes differ from chemical changes and the material recovers its original properties if the change is reversed. 3. Use the particle model to describe how heating a system will change the energy stored within the system and raise its temperature or produce changes of state. 4. Explain how the motion of the molecules in a gas is related both to its temperature and its pressure: hence explain the relationship between the temperature of a gas and its pressure at constant volume. (qualitative only)