Particle Model of Matter

• States of Matter

  . There are three states of matter: solids, liquids and gases

  . Solids and liquids are incompressible (cannot be squashed) because there are no gaps between the particles in them

  . Solids contain particles in a fixed pattern and have a fixed size and shape

  . Liquids have a fixed size but contain particles that are free to move, allowing them to change shape to fit their container

  . Gases have large gaps between the particles, making them compressible and enabling them to change size and shape
• Density

  . The density of a material is its mass per unit volume
• Investigate the density of regular and irregular solids and liquids

  1. Set the equipment up

  2. Record the height of the water in the measuring cylinder and the mass of the solid/liquid being tested

  3. Add the solid/liquid being tested to the measuring cylinder

  4. Record the new height in the measuring cylinder

  5. Subtracting the original height from the new height gives the volume of the solid/liquid being tested

  6. Now the density can be calculated
• Considerations, Mistakes and Errors

  • If a solid that is less dense than water is tested, the volume measurement will be incorrect because the solid will not be fully submerged
  • When reading from the measuring cylinder, the reading should be taken from the bottom of the meniscus
  • The temperature of the water must be exactly the same throughout all tests, as an increase in temperature could cause the material or water to change volume slightly through expansion
• Variables

  • The independent variable is the material being tested
  • The dependent variables are the volume and mass
  • The control variable is the temperature
• Hazards and risks

  • There are very few hazards, unless the materials being tested are hazardous or react with water
  • The main hazard could be a slip hazard if water is spilt
• As energy is added to a system

  Its temperature will increase
• At the melting or boiling point, the energy being added causes the substance to change state not temperature
• A change of state is reversible
• Change of state

  A physical change that alters the internal energy but not the temperature or mass. It is not a chemical change
• Latent heat of fusion

  The energy needed for a substance to change from solid to liquid (melt)
• Latent heat of vaporisation

  The energy needed for a substance to change from liquid to gas (evaporate)
• Heating and cooling graphs

  Horizontal parts indicate where energy is being used to change state
• At certain pressures, some substances have a boiling point that is the same or lower than their melting point
• Sublimation

  Substances change from a solid to a gas without having a liquid phase in the middle
• Desublimation

  The reverse process, changing from a gas to a solid
• Key Point

  The energy needed to cause 1kg of a substance to change state is called its specific latent heat
• Particle Motion and Pressure in Gases

  . The particles of a gas are in constant random motion and its temperature is related to the average kinetic energy of the particles

  . When the particles of a gas collide with the walls of their container they exert a force on the wall, which is felt as pressure

  . If the volume is kept constant, increasing the temperature increases the speed of the particles. This increases the frequency and force with which the particles hit the walls and increase the pressure