3.1 Particle M of M

• density = mass / volume
• specific latent heat = amount of energy needed to raise the temperature of 1kg substance by 1 degree C
• latent heat = energy needed to change the state of a substance
• specific latent heat = the amount of energy needed to change 1kg of a substance from one state to Another without changing the temperature.
• specific latent heat of fusion = latent heat of changing between a solid and a liquid
• specific latent heat of vaporization = the specific latent heat of changing between a liquid to a gas
• heating can do two things

  increase the temperature

  change the state
• heating graphs

  bonds between particles are broken

  internal energy is transferred to particles potential energy store

  temperature stays the same
• cooling graphs

  stronger bonds between particles

  internal energy decreases energy transferred away

  temperature stays the same
• To calculate density, the volume of the material must be known. If the object is a regular shape, the volume can be found by using a ruler
• If the object has an irregular shape, the volume can be measured using a displacement can.
• Method 3: Water (or any liquid)

  1. Place the measuring cylinder on the top pan balance and measure its mass.
  2. Pour 50 cm3 of water into the measuring cylinder and measure its new mass.
  3. Subtract the mass in step 1 from the mass in step 2. This is the mass of 50 cm3 of water.
  4. Use the measurements to calculate the density of the water.
• Method 2: Stone or other irregular shaped object

  1. Place the stone on the top pan balance and measure its mass.
  2. Fill the displacement can until the water is level with the bottom of the pipe.
  3. Place a measuring cylinder under the pipe ready to collect the displaced water.
  4. Carefully drop the stone into the can and wait until no more water runs into the cylinder.
  5. Measure the volume of the displaced water.
  6. Use the measurements to calculate the density of the stone.
• Method 1: Regular solids

  1. Use a ruler to measure the length (l), width (w) and height (h) of a steel cube.
  2. Place the steel cube on the top pan balance and measure its mass.
  3. Calculate the volume of the cube using (l × w × h).
  4. Use the measurements to calculate the density of the metal.
  5. Use vernier callipers to measure the diameter of the sphere.
  6. Place the metal sphere on the top pan balance and measure its mass.
  7. Calculate the volume of the sphere using 43𝜋(𝑑2)3
  8. Use the measurements to calculate the density of the metal.
• • Chemical bonds between the particles may form, break or stretch. There is a change in the chemical potential store of energy in the material.
  • The material will heat up or cool down as the particles within it gain or lose speed. There is a change in the thermal store of energy within the material.
• 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 is a measure of the total energy of all the particles in the object or substance. This includes the kinetic energy of the particles and chemical potential energy of the bonds between them.
• • Temperature is a measure of the average speed of the particles. This is based on the kinetic energy of individual particles.
• From this it can be seen that a change in temperature of a system depends on:

  • the mass of the material
  • the substance of the material
  • the amount of energy put into the system
• change in thermal energy = mass × specific heat capacity × temperature change
• • the energy required for a particular change in temperature is given by the specific heat capacity
  • the energy required for a particular change in state is given by the specific latent heat
• change in thermal energy = mass × specific latent heat
• pressure = force / area
• As the temperature increases, the pressure increases showing that pressure is directly proportional to temperature.
• pressure × volume = constant
• If the temperature of a gas stays the same, the pressure of the gas increases as the volume of its container decreases. This is because the same number of particles collides with the walls of the container more frequently as there is less space. However, the particles still collide with the same amount of force.
• • increasing the temperature - this increases the force of each collision
  • decreasing the volume - this increases the number of collisions per second
• work done = force × distance