Particle model of matter
Density
The compactness of a substance
Density (Kg/m3) = Mass (kg) / volume(m3)
The density of an object depends on how its particles are arranged and the space between them
A dense material has its particles packed tightly together
In a less dense material, the particles are more spread out
Is you compressed a material, you wouldn't be changing it's mass, you would be decreasing its volume
Particle arrangement
Solid
Strong forces of attraction
regular arrangement
Particles can only vibrate about their fixed positions
Density is generally highest in this state as the particles are closest together
Liquids
Weaker forces of attraction
Particles are close together and can move past eachother
Irregular arrangement
Particles have more energy than in a solid, move in random directions at low speeds
Generally less dense than solids
Gas
Almost no forces of attraction
Particles have more energy than liquids and solids, free to move
Particles travel in random directions at high speeds
Generally less dense than liquids
1g/cm3 = 1000Kg/m3
ρ = m/v
Measuring the density
Internal energy
Particles in a system vibrate, they have energy in their kinetic energy stores due to their individual motion
They also have energy in their potential energy stores due to the energy between particles
Internal energy is the total energy that its particles have in their kinetic and potential energy stores
Internal energy = kinetic energy + potential energy
Heating the system transfers energy to its particles, they gain kinetic energy, which increases the internal energy
A change in state occurs if the substance is heated enough, the particles will have enough kinetic energy to break the bonds holding them together
An increase in potential energy means that the bonds are breaking and there is a change of state
Specific latent heat
The energy that must be transferred to change 1Kg of a material to one state of matter to another without a temperature change
Specific latent heat of fusion
When the change of state is between a solid and a liquid
During melting or freezing
Specific latent heat of vaporisation
When the change of state is between a liquid and a gas
During boiling or condensation
Involve a change of state, never a change in temperature since changes of state occur at a constant temperature
Equation
Thermal energy for change in state (J) = mass (kg) X Specific latent heat (j/kg)
E = ml
Pressure in gases
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
Decreasing the volume of a gas means that the particles will collide more frequently with the walls, the pressure increases
As the pressure increases, the volume must decrease as long as the temperature of the gas and the mass is constant (Boyle's law)
For a fixed mass of gas at a constant temperature
Pressure X volume = constant
Pressure is measure in pascals (Pa)
P1V1 = P2P2
Used to calculate the new pressure and volume for a fixed mass of a gas at a constant temperature
liquid
Place a measuring cylinder on a balance and zero it
Pour 50ml of the liquid into the measuring cylinder, and record it's mass
Calculate the volume of the liquid, 1ml = 1cm3
Find the density using ρ = m/v
Solid
Measure the object's mass using a balance
For a regular solid: measure its length width and height to calculate its volume
For an irregular solid: Submerge in a eureka can filled with water, the volume of water displaced in the measuring cylinder is the volume of the object
Plus the object's mass and volume into the formula ρ= m/v to find it's density
Doing work on a gas
If you transfer energy by applying a force then you do work
Doing work on a gas increases its internal energy, which can increase the temperature
Adding more particles to a fixed volume
Pumping more gas into the same volume means more particle are present
More collisions occur per unit time with the wall, so pressure increases
Energy is transferred to the particles when more gas is added into the fixed volume, so this heats the gas
Fixed number of particles for a smalle volume
Particles collide with the wall moving inward
Particles gain momentum, as the rebound velocity is greater than the approaching velocity
So as the particle has a greater velcoty, the pressure increases as the particles collide with the walls more frequently
As temperature increases, the kinetic energy of each particle increases