States of Matter

• Solids

  • Solids have a fixed volume and shape and they have a high density.
  • The atoms vibrate in position but can’t change location
  • The particles are packed very closely together in a fixed and regular pattern
• Liquids

  • Liquids also have a fixed volume but adopt the shape of the container
  • They are generally less dense than solids (an exception is water), but much denser than gases
  • The particles move and slide past each other which is why liquids adopt the shape of the container and also why they are able to flow freely
• Gases 

  • Gases do not have a fixed volume, and, like liquids, take up the shape of the container
  • Gases have a very low density
  • Since there is a lot of space between the particles, gases can be compressed into a much smaller volume
  • The particles are far apart and move randomly and 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)
• Solid

  Arrangement | Regular arrangement

  Particle Movement | Vibrate about a fixed position

  Particle Closeness | Very close

  Density | High

  Particle Energy | Low energy

  
• Liquid

  Arrangement | Random arrangement

  Particle Movement | Move around each other

  Particle Closeness | Close

  Density | Medium

  Particle Energy | Greater than solid, less than gas

  
• Liquid

  Arrangement | Random arrangement

  Particle Movement | Move quickly in all directions

  Particle Closeness | Far apart

  Density | Low

  Particle Energy | Highest energy

  
• The state changed

  A) Evaporation

  B) Condensation

  C) Sublimation

  D) Desublimation

  E) Melting

  F) Freezing

  G) Energy

  
• Melting

  • Melting is when a solid changes into a liquid
  • Requires heat energy which transforms into kinetic energy, allowing the particles to move
  • Occurs at a specific temperature known as the melting point (m.p.) 
• Freezing

  • Freezing is when a liquid changes into a solid
  • 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. Water, for example, freezes and melts at 0 ºC
  • Requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature 
• Boiling

  • Boiling is when a liquid changes into a gas
  • 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
  • Occurs at a specific temperature known as the boiling point (b.p.)
• Evaporation

  • Evaporation occurs when a liquid changes into a gas and occurs over a range of temperatures
  • 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
  • The larger the surface area and the warmer the liquid surface, the more quickly a liquid can evaporate
• Condensation

  • Condensation occurs when a gas changes into a liquid on cooling and it takes place over a range of temperatures
  • 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
• ⇌


  The process can go forwards and backwards
• • When substances are heated, the particles absorb thermal energy which is converted into kinetic energy
  • This is the basis of the kinetic theory of matter
• • Heating a solid causes its particles to vibrate more
  • As the temperature increases, the particles vibrate so much that the solid expands until the structure breaks
  • This is when the solid melts into a liquid
• • Heating a liquid causes its particles to move more and spread out
  • Some particles at the surface gain sufficient energy to overcome the intermolecular forces
  • This is when a liquid starts to evaporate
  • When the boiling point is reached, all of the particles gain enough energy to escape and the liquids boils into a gas
• Changes in state can be shown on a graph called a heating curve

  A) temperature

  B) state

  
• Pressure & temperature in gases

  • A change in temperature or pressure affects the volume of gases
  • As the air inside a hot air balloon is heated up, it expands and the balloon gets bigger
  • This is because the volume of a gas increases as temperature increases
• If you have a gas stored inside a container that is squeezed, the pressure increases as you decrease the volume
• Gases & kinetic theory

  • Gaseous particles are in constant and random motion
  • The pressure that a gas creates inside a closed container is produced by the gaseous particles hitting the inside walls of the container:

  
• How does temperature affect the volume of a gas?

  • Increasing the temperature increases the kinetic energy of each particle
  • Remember: The thermal energy from increasing the temperature is converted to kinetic energy in the particles
  • As the temperature increases, the particles in the gas move faster and spread out more
  • If the gas particles are inside a container, they will collide with the container walls more frequently
  • If the container walls are flexible and stretchy then the container will get bigger and bigger, just like the hot air balloon!
• How does pressure affect the volume of a gas?

  • Pressure is about the number of particles in a given volume
  • Increasing the pressure means that there are the same number of particles but in a smaller volume
  • Conversely, decreasing the pressure means that there are the same number of particles but in a larger volume

  
• Diffusion

  • Diffusion occurs in gases and liquids, due to the random motion of their particles
  • It is where particles move from an area of high concentration to an area of low concentration
  • Eventually the concentration of particles is even as the particles are evenly spread throughout the available space
  • Diffusion happens on its own and no energy input is required
  • Although, it occurs faster at higher temperatures because the particles have more kinetic energy
• Diffusion in liquids

  A) from a region of high to low concentration

  B) equilibrium

  C) particles now evenly spread through the solution

  
• Diffusion in gases

  • Diffusion is faster in gases than in liquids
  • This is because gaseous particles have more energy and move quicker than liquid particles
  • For example, the diffusion of bromine gas and air:
  • At the start, the orange-brown bromine gas is an area of high concentration
  • It diffuses from a high to low concentration
  • After 5 minutes, the bromine gas will have diffused from the bottom jar until it is evenly spread throughout both jars
  • The same can be said for the air, although it is less obvious as it is colourless

  
• How molecular mass affects diffusion

  • At the same temperature, different gases do not diffuse at the same rate.
  • This is due to the difference in their relative molecular masses
  • Gases with a lower relative molecular mass are "lighter" which means that they:
  • Travel faster
  • Travel further in the same amount of time
  • The reverse argument is true for gases with a high relative molecular mass, they:
  • Travel slower
  • Do not travel as far in the same amount of time
  • For example, the reaction between ammonia and hydrogen chloride
• Ammonia molecules have less mass than HCl molecules so they diffuse faster and the product forms closer to the HCl end

  A) hcl end