Particle Model of Matter

• Density = mass/volume
• The particle model can explain density and the 3 states of matter
• Density is a measure of the compactness of a substance
• Density depends on the spacing of the atoms in matter
• Solids and liquids have similar densities as the space between particles does not change significantly
• Usually liquids have a lower density than solids (main exception is ice and water)
• Gases have a far lower density than solids and liquids
• The spacing between atoms increase x10, as the particles have lots of energy to move, so volume increases greatly and therefore the density decreases greatly compared to solids/liquids
• Mass is conserved during a change of state
• Energy which is stored by particles (atoms and molecules) within a system o the energy takes the forms of: Kinetic Energy (vibration of atoms etc.) Potential Energy (between the particles)
• Heating a System - Heating increases the energy the particles have - This increases the internal energy o This either raises the temperature of the system o Or produces a change of state
• Specific heat capacity - The amount of energy required to raise the temperature of 1kg of a substance by 1°C.
• change in thermal energy = mass × specific heat capacity × temperature change
• Specific Latent Heat - The amount of energy needed to change the state of 1kg of a substance without a change in temperature
• Specific Latent Heat of fusion is energy to melt/freeze Specific Latent Heat of vaporisation is energy to boil/condense
• energy for a change of state = mass × specific latent heat
• The molecules of a gas are in constant random motion.
• The temperature of the gas is related to the average kinetic energy of the molecules.
• The higher the temperature, the greater the average kinetic energy and so the faster the average speed of the molecules.
• When the molecules collide with the wall of their container they exert a force on the wall.
• The total force exerted by all of the molecules inside the container on a unit area of the walls is the gas pressure.
• Changing the temperature of a gas, held at constant volume, changes the pressure exerted by the gas (known as the Pressure law).
• Changing the volume of a gas affects the pressure
• A gas can be compressed or expanded by pressure changes. The pressure produces a net force at right angles to the wall of the gas container (or any surface).
• Increasing the volume in which a gas is contained, at constant temperature, can lead to a decrease in pressure (known as Boyle’s law), this is due to the reduced number of collisions per unit area.
• PV = constant
• Work done = force x distance