p6 molecules and matter

• density is the mass per unit volume
• if an object has a higher density than the liquid it will sink
• if an object has a lower density than the liquid it will float
• when a substance changes state the mass stays the same because the number of particles present stays the same
• when a substance changes state the arrangement of the particles changes and they move with more kinetic energy
• the further apart substances are the less dense the substance is
• when the temperature of the substances is increased the particles vibrate faster
• in solids the particles are held next to each other in fixed positions which they vibrate in to keep the shape of the solid
• in liquids the particles are in contact with each other but move about at random so a liquid doesn't have its own shape and can flow
• in a gas the particles aren't touching and move about randomly and faster so the density is much lower than in solids and liquids
• the solid has the highest density because there are strong forces that keep the particles close together
• the temperature is constant during changes of state
• latent heat is the energy that is taken in or given out when a substances changes state
• latent heat of fusion is when a substance changes from solid to liquid
• latent heat of vaporisation is when a substance changed from liquid to gas
• during evaporation, molecules gain energy and the faster molecules break away from the attraction of the others and escape
• after evaporation the liquid is cooler because the average kinetic energy of the remaining molecules in the liquid has decreased
• condensation is when a gas comes into contact with a cool surface and turns back into a liquid
• the surface area and temperature of a liquid and a draught of air across the liquid effect the rate of evaporation
• the surface area and temperature effect the rate of condensation
• internal energy is the energy stored by particles due to their position and motion
• the internal energy is the sum of energy in all the individual particles in a substance
• internal energy = kinetic energy + potential energy
• increasing the temperature increases the internal energy because the particles start to move away from each other and vibrate faster increasing the potential energy and increasing kinetic energy
• the specific latent heat of a substance tells you how much energy is needed to change the state of 1kg of the substance at a constant temperature
• for a fixed volume of gas if the particles increase in temperature they gain kinetic energy so the collide more frequently and the pressure increases
• for a fixed temperature of gas if the volume is decreased the particles are closer together so the particles collide more frequently and the pressure increases
• 'work' needs to be done to compress a gas to overcome the force due to the gas' pressure
• Boyels law: pressure of gas is inversely proportional to its volume at a constant temperature and mass. As pressure increases volume decreases at the same rate