Topic 14 - Particle Model

• Change in Thermal Energy: The product of the mass, specific heat capacity and temperature change of a substance
• • Chemical Changes: Changes to the chemical structure of a substance, the substance does not usually restore its original properties when the changes are reversed
• • Condensation: The changing from vapour state to a liquid state, when a substance is cooled
• • Density: The mass per unit volume of an object
• • Evaporation: The changing from liquid state to a vapour state, when a substance is heated
• • Freezing: The changing from a liquid state to a solid state, when a substance is cooled
• • Gas Temperature: The temperature of a gas is directly proportional to the average kinetic energy of its molecules
• • Internal Energy: The energy stored by the atoms and molecules that make up a system, it is equal to the sum of the total kinetic and potential energies of the particles in the system
• • Latent Heat: The energy required for a substance to change state
• • Melting: The changing from solid state to liquid state, when a substance is heated
• • Pascals: The unit of pressure, equal to a force of one Newton acting perpendicular to an area of one metre squared
• • Physical Changes: Changes to the physical properties of a substance which can be reversed, changes of state are physical changes since substances can restore their original properties when the changes are reversed
• • Pressure: The force acting perpendicular to a surface, per unit area
• • Specific Latent Heat of Fusion: The amount of energy needed to change the state of one kilogram of a substance from solid state to liquid state, whilst held at constant temperature
• • Density depends on the spacing of the atoms in matter, with solids and liquids having similar densities as the space between particles does not change significantly.
• Specific Latent Heat of Vaporisation: The amount of energy needed to change the state of one kilogram of a substance from liquid state to vapour state, whilst held at constant temperature
• • Gases have a far lower density as the spacing between atoms increases due to the particles having lots of energy to move, therefore volume increases greatly and the density decreases greatly compared to solids/liquids.
• Changes of state involve changes in volume and pressure, with mass being the same.
• • The particles gain momentum, as the rebound velocity is greater than the approaching velocity.
• • As the particle has a greater velocity, the pressure increases as the particles collide with the walls more frequently, and the temperature also increases, as the kinetic energy of each particle increases.
• Energy is transferred to the particles when more gas is added into the fixed volume, heating the gas.
• • Specific Latent Heat: The amount of energy needed to change the state of one kilogram of a substance, whilst held at constant temperature
• • Sublimation: The direct changing of a substance from a solid state to a vapour state, without passing through the liquid phase
• • Mass is conserved during a change of state, meaning if 20g of liquid evaporates, the gas produced will also weigh 20g.
• Internal energy is energy which is stored by particles (atoms and molecules) within a system, taking the forms of kinetic energy and potential energy.
• • Heating a system increases the energy the particles have, which increases the internal energy.
• Changing the temperature of a gas, held at constant volume, changes the pressure exerted by the gas, known as the Pressure law.
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  • Gases have a far lower density as the spacing between atoms increases due to the particles having lots of energy to move, therefore volume increases greatly and the density decreases greatly compared to solids/liquids.
• Physical changes are reversible and not chemical changes as the material retains its original properties when reversed.
• • Internal energy is energy which is stored by particles (atoms and molecules) within a system, taking the forms of kinetic energy and potential energy.
• Heating a system increases the energy the particles have, which increases the internal energy.
• Density = Mass / Volume
• Solids, close together, regular pattern, vibrate about a fixed position
• Liquid, close together, random, move around each other,
• gas, far apart, random, move quickly in any direction
• Most substances are the most dense when they are in solid form and the least dense when they are in a gaseous form. This is due to the arrangement of the molecules; with solids' molecules being closer together and gases being far apart.
• When substances melt, freeze, evaporate, boil, condense or sublimate, mass is conserved. These physical changes differ from some chemical changes because the material recovers its original properties if the change is reversed.
• Heating a system will cause the energy stored within the system will change and raise its temperature as heating a system causes thermal energy to be stored. The more energy being stored means the speed of the vibrating particles increases. 
• If enough energy is being stored, the particles vibrate fast enough in order to break the molecular forces between particles, causing changes in state.
• Temperature is a measure of the movement of particles.