chem testing

• Kinetic Theory of Matter


  A model that helps us imagine how matter is arranged and how it behaves, and how this arrangement relates to the properties of the three states of matter
• Kinetic Theory of Matter

  • All matter is made up of very tiny particles, which can not be seen by the naked eye
  • Different substances are available as different types of particles (atoms, molecules or ions)
  • The particles move all the time
  • The higher the temperature the faster they move on average
  • Heavier particles move more slowly than lighter ones at any given temperature
• Solids


  • Strong forces of attraction between particles, particles are packed very closely together in a fixed and regular pattern
  • Atoms vibrate in position but can't change position or move
  • Solids have a fixed volume, shape and high density
• Liquids


  • Weaker attractive forces in liquids than in solids, particles are close together in an irregular, unfixed pattern
  • Particles can move and slide past each other which is why liquids adopt the shape of the container they're in and also why they are able to flow
  • Liquids have a fixed volume but not a fixed shape and have a moderate to high density
• Gases


  • No intermolecular forces, particles are in random movement and so there is no defined pattern
  • Particles are far apart and move quickly (around 500 m/s) in all directions, they collide with each other and with the sides of the container (this is how pressure is created inside a can of gas)
  • No fixed volume, since there is a lot of space between the particles, gases can be compressed into a much smaller volume. Gases have low density
• Melting


  1. Melting is when a solid changes into a liquid

  2. Requires heat energy which transforms into kinetic energy, allowing the particles to move

  3. Occurs at a specific temperature known as the melting point (m.p.) which is unique to each pure solid
• Boiling


  1. Boiling is when a liquid changes into a gas

  2. Requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and within the liquid

  3. Occurs at a specific temperature known as the boiling point (b.p.) which is unique to each pure liquid
• Freezing


  1. Freezing is when a liquid changes into a solid

  2. This is the reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same

  3. Requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature which is unique for each pure substance
• Evaporation


  1. When a liquid changes into a gas. Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquid's surface at low temperatures, below the b.p. of the liquid

  2. The larger the surface area and the warmer the liquid/surface, the more quickly a liquid can evaporate

  3. No heat is required and evaporation occurs over a range of temperatures
• Condensation


  1. When a gas changes into a liquid, usually on cooling. When a gas is cooled its particles lose energy and when they bump into each other they lack the energy to bounce away again, instead they group together to form a liquid

  2. No energy is required for condensation to occur and it takes place over a range of temperatures

  
• Sublimation


  1. When a solid changes directly into a gas

  2. This happens to only a few solids such as iodine or solid carbon dioxide

  3. The reverse reaction also happens and is also called sublimation (sometimes called deposition or desublimation)

  4. Sublimation occurs at a specific temperature which is unique for a pure substance
• Gaseous particles are in constant and random motion
• Increasing temperature


  Increases the kinetic energy of each particle, as the thermal energy is transformed to kinetic energy, so they move faster
• Decreasing temperature


  Has the opposite effect, decreasing the kinetic energy of the particles
• Pressure of a gas

  Produced by the gaseous particles hitting the inside walls of the container. As the temperature increases, the particles in the gas move faster, impacting the container's walls more frequently
• Increasing temperature


  Causes an increase in pressure
• Increasing pressure on a gas at fixed temperature

  Decreases the volume of the gas
• Increasing temperature


  Increases the volume of a gas
• Decreasing temperature


  Decreases the volume of a gas
• Heating Curve


  1. From A to B: Increasing heat energy increases vibration of the solid particles so the temperature of the solid increases

  2. From B to C: Increasing heat weakens the forces of attraction between particles so they begin to slide over each other, there is no temperature change because all energy supplied is used to overcome the forces between the particles, the substance melts

  3. From C to D: Increasing energy increases the motion of the particles in the liquid so the temperature of the liquid increases

  4. From D to E: Forces of attraction between liquid particles weakens so particles start to move away from each other, there is no temperature change as the energy supplied is used to break the forces between the particles, the substance boils

  5. From E to F: Increasing energy increases the speed of the gas particles, so the temperature increases and the gas particles are getting far away from each other
• Cooling Curve is the opposite of the Heating Curve
• Diffusion


  • The process by which different gases or different liquids mix and is due to the random motion of their particles
  • Diffusing particles move from an area of high concentration to an area of low concentration
  • Eventually the concentration of particles is even as they spread out to occupy all of the available space
  • Diffusion happens on its own and no energy input is required although it occurs faster at higher temperatures
• Relative molecular mass of a gas

  • The greater the relative molecular mass, the slower the rate at which the gas will diffuse
  • The smaller the relative molecular mass, the faster the rate at which the gas will diffuse
• Gases to be placed in order of fastest to slowest diffusion rate

  • Hydrogen (H2)
  • Methane (CH4)
  • Chlorine (Cl2)
• Temperature


  An increase in temperature will increase the average kinetic energy of the particles, causing them to move faster and therefore diffuse at a greater rate
• Diffusion can also take place in liquids and solutions because the particles do not have a fixed position - they are able to slide past each other and therefore move from one side of a container to the other
• Diffusion occurs much faster in gases than in liquids as gaseous particles move much quicker than liquid particles
• At the same temperature, different gases do not diffuse at the same rate due to the difference in their relative molecular masses
• Lighter gas particles can travel faster and hence further, therefore the lower its relative mass the faster a gas will diffuse
• Diffusion of NH3 and HCl gases

  • NH3 molecules have less mass than the HCl molecule, so diffuse faster, hence the product (a white cloud of NH4Cl) forms closer to the end where the HCl is