particle model of matter

Created by

Alice Stothart

Cards (31)

density: amount of mass per unit volume
density
there is little difference between the desnity of a solid and its corresponding liquid, this is because both are tightly packed
the same number of particles in a gas, with the same volume to cover, will spread further apart
> less dense than its corresponding solid and liquid
density calculations
density = mass / volume
it can be measures in either (g/cm^3) or (kg/m^3)
required practical - density
volume
volume can be measured by measuring the shape, and if irregular, by measuring the displacement
measure the mass of the object
fill a eurika can with water, up to the brim of the spout
place a beaker under the spout to catch displaced water
lower object in (on string)
pour the displaced water into measuring cylinder
measure the volume
changes of state
boiling - active process, because you have to put (internal) energy into the liquid to turn it into a gas
evaporation - passive process, because the liquid absorbs energy from the surroundings, so some of its particles gain enough energy to escape from the liquid
both of these are liquid to gas, just done differently
changes of state are physical processes because they can be reversed and no new products are formed
internal energy
when a material is heated or cooled, two things happen:
chemical bonds may form, break or stretch
there is a change in the chemical potential energy
as the material heats or cools, the particles will speed up or slow down
there is a change in the thermal energy store
the internal energy is the total amount of kinetic energy and chemical potential energy
internal energy
When the substance melts or boils, energy is put in to breaking the bonds that are holding particles together, which increases the potential energy
internal energy
the law of conservation means (assuming no energy is lost to the surroundings), energy will be transferred between the chemical store and the thermal store of the internal energy
energy is linked to the temperature of the material, but they are very different:
internal energy: the measure of the total energy of all the particles in a substance, this includes the kinetic energy of the particles and the chemical potential energy of the bonds between them
temperature: a measure of the average speed of the particles, it is based on the kinetic energy of the individual particles
when heating a substance
takes more energy to raise the temperature of a larger substance, because more particles have changed speed
specific heat capacity: the amount of energy needed to increase 1kg of substance by 1.C
the specific heat capacity of water is 4,200J
specific heat capacity
the amount of energy stored or released by a substance can be calculated using the formula:
ΔE = m c ∆θ
change in thermal/internal energy (J) = mass(kg) x SHC(J/kg'C) x change in temperature ('C)
specific latent heat
changing the internal energy of a material causes it to change temperature or state:
energy required for a particular change in temperature is given by the specific heat capacity
energy required for a particular change in state is given by the specific latent heat
specific latent heat
specific latent heat: the amount of energy required to change the state of 1kg of substance without changing its temperature
> the energy is used to change the state rather than increasing the kinetic energy and temperature
specific latent heat, of fusion and of vaporisation
latent heat of fusion: the amount of energy required to melt or freeze the material at its melting point
to do with liquids and solids
latent heat of vaporisation: the amount of energy required to boil or condense the material at its boiling point
to do with liquids and gases
calculating thermal energy changes
ΔE = m x l
change in thermal energy (J) = mass (Kg) x specific latent heat (J/Kg)
heating and cooling graphs
the horizontal line is where energy is not being used to increase the speed or temperature of the particles, but instead is being used to break the bonds between the particles and change the state
the longer the horizontal line, the more energy is used to cause the change of state
the amount of energy represented by the horizontal lines is equal to the latent heat
If a change in internal energy of a material will cause it to change temperature and change state, both equations can be used.
particle motion
particles in a gas move quickly and in all directions
the speeds of the individual particles vary, but overall they move quicker than they do in solids or liquids
> doesn't take long for gas particles to spread out and fill a container
gas pressure
gas particles move quickly and in all directions
> collide frequently (between particles or walls)
the force acting on the container due to these collisions is at right angles to the container....
calculating pressure caused by a gas
p = F / a
pressure(N/m^2) = force(N) / area(m^2)
pressure and temperature
the pressure of a gas will increase as its temperature increases, i the volume of the gas and the container stays the same.
temperature is a measure of the average kinetic energy of its particles
if the temperature is increased
the particles will gain more kinetic energy, collide more frequetly, and with more force
as the temperature increases, the pressure increases
> pressure is directly proportional to temperature
pressure and volume
as the volume decreases the pressure increases (ie: if you squeeze a balloon)
pressure and volume
robert boyle first investigated the relationship between pressure and volume
his experiment gave one of the first peices of experiemental evidence for particle theory
he poured mercury into a J - shaped tube which was sealed at one end
he was able to trap an air bubble
he then poured in more mercury slowly
he saw that the greater the volume of mercury, the more pressure the air bubble was experiencing, and the smaller the bubble became
boyle showed that volume is inversely proportional to pressure
the pressure of a gas increases if the volume of the container deacreases, if the temperature remains the same
for a fixed mass of gas at a constant temperature:
p V = constant
pressure (Pa - pascals) x volume(m^3) = constant
The change in volume or pressure for gas at a constant temperature can be calculated using the equation:
𝑝1𝑉1=𝑝2𝑉2
p1 and V1 are the pressure and volume before either are changed, p2 and V2 are the pressure and volume after the change.
pressure can be increased by:
increasing the temperature - increases the force of each collision
decreasing the volume - increases the number of collisions per second
boyle concluded that the volume could only be inversly proportional to the pressure for a fixed mass of gas and a constant temperature
and only if the gas contained particles which were moving
this led to a discovery which triggered the industrial revolution
forces applieed to the particles in a gas result in an energy transfer
Since the volume of the gas has decreased, the pressure increases because the particles are moving in less space and collide more often. The temperature of the gas is not fixed in most applications and the increased pressure leads to an increase in temperature.