3 - Particle Model of Matter

• 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
• Density is defined as the mass per unit volume, represented by the symbol ρ, in kilograms per metre cubed, kg/m^3.
• 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.
• A fixed number of particles occupy a smaller volume.
• The particles collide with the wall which is moving inward.
• 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.
• 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.
• Changing the temperature of a gas, held at constant volume, changes the pressure exerted by the gas, known as the Pressure law.
• Increasing the volume in which a gas is contained, at constant temperature, can lead to a decrease in pressure, known as Boyle’s law, due to the reduced number of collisions per unit area.
• The temperature of ice can be represented as: A - Solid, B - 0 °C, C - No temperature change, D - Liquid, E - Boiling.
• Gas pressure is the force exerted by all of the molecules inside the container on a unit area of the walls.
• Increasing the volume of a container will lead to a decrease in pressure.
• Doing work on a gas increases its temperature.
• The pressure P is in pascals, Pa, and the volume, V, in metres cubed, m3.
• Evaporation takes more energy than condensation, hence it takes longer.
• Sublimation is when solid goes straight to gas, as seen in "dry ice" (solid CO2).
• A gas can be compressed or expanded by pressure changes.