PARTICLE MODEL OF MATTER

Density

  • Density is how mass a substance has per unit of it’s volume

  • Density(kg/m3) = mass/volume — p=m/v

  • Calculating density of liquids - record the mass on a balance, measure the volume in a cylinder and calculate

  • Calculating density of solids - first measure the mass of a balance

    • For regular solids, measure the length, height and width and calculate

    • For irregular, fill a eureka can with water and place the solid in it - the volume of water that is displaced = volume

  • Generally, the larger the volume = a more accurate density, as it minimises the effects of uncertainty

    • Can also repeat and use a mean to reduce uncertainty

Specific heat capacity

  • Specific heat capacity is the amount of energy required to raise one kilogram of a material by one degrees Celsius - in J/kg degrees c

  • Specific heat capacity depends on the mass, substance of material and the amount of energy put into the system

  • Solids have a lower specific heat capacity than liquids

    • The particles are closer together and more likely to hit each other and pass the energy around

  • Change in thermal energy = mass x specific heat capacity x temperature

  • ΔEt (J)= m (kg)x c (J/kg°)x Δtemp (°c)

Specific latent heat

  • Specific latent heat is the amount of energy required to change the state of 1kg of a material without changing it’s temperature

  • Changing the internal energy of a material causes either a temperature of STATE change - specific latent heat

  • Every material has 2 specific latent heat values

    • Latent heat of fusion - melt/freezing

    • Latent heat of vaporisation - boil/condensing

    • For example, the latent heat of fusion for water is 334 kJ/kg, and is 2260 kJ/kg for latent heat of vaporisation

  • Change in potential energy = mass x specific latent heat

    • ΔE (J) = m (kg) x l (J/kg)

  • Horizontal lines on internal energy graph ↓

Particle motion in gases

  • Particles in a gas move in random directions in a straight line unless another particle hits it (or a wall)

  • They rebound when they hit a wall, which exerts a force and creates pressure

Pressure in gases

  • Total pressure depends on the number of collisions and how much energy each collision involves

    • Depends on temperature, concentration and volume

  • In a flexible container (like a balloon), the temperature and concentration will increase the volume

  • In a solid container:

    • Temperature - if you heat up the gas, it’s energy will increase, so there is more kinetic energy and the particles will move faster

      • This means there are more collisions, with more force, creating a higher pressure

    • Concentration - if you increase the number of particles in the same volume, the concentration increase and there are more particles to collide with, which causes more collisions and increases the pressure

    • Volume - if the volume is decreased, there will be more particles per unit of volume, which causes more collisions and a higher pressure

Increasing pressure of a gas

  • We can increase the pressure of a gas by:

    • Increasing the no. of particles

    • Decreasing the volume

    • Increasing the temperature

  • Pressure and volume are inversely related

    • Pressure increases = volume decreases

    • Pressure decreases = volume increases

  • Pressure x volume = constant value (if temperature is constant)

    • pV = constant

Internal energy

  • Internal energy is the total amount of kinetic and chemical potential energy of all particles in a system

  • When a material is heated or cooled, two changes can happen

    • Chemical bonds between the particles form or break (between states)

    • Thermal energy store changes as particles speed up or slow down (‘in’ states)

  • As the temperature increases, particles kinetic energy increases. When the substance melts, the energy is put into breaking bonds, which increases chemical potential energy

  • Conservation of energy shows that any energy transferred will be distributed between the chemical store and thermal store

  • When bonds break, the speed of the particles increase to overcome more bonds to further change state

  • Horizontal represents increasing chemical energy, and increasing temp shows increase in kinetic/thermal energy

Changing states