Chemistry- States of Matter

• Three states of matter: solids, liquids, and gases
• Arrangement of particles in solids:

  • Particles are arranged regularly and packed closely together
  • Particles can only vibrate about fixed positions
  • Strong forces of attraction between particles keep them together
• Arrangement of particles in liquids:

  • Particles are mostly touching, but some gaps have appeared
  • Less effective forces between particles
  • Particles can move around each other
  • Particles are arranged randomly
• Arrangement of particles in gases:

  • Particles are moving randomly at high speed in all directions
  • Particles are much further apart
  • Almost no forces of attraction between particles
  • Particles have more kinetic energy than in liquids and solids
• Changing state between solid and liquid:

  • Heating a solid makes particles vibrate faster until they can move around each other, forming a liquid
  • Temperature at which solid melts is called melting point
  • Energy must be supplied to convert a solid to a liquid
  • Cooling a liquid makes particles move more slowly until they form a solid, called freezing
  • Temperature at which liquid freezes is the freezing point
  • Melting point and freezing point temperatures are the same
• Boiling:

  • Occurs when a liquid is heated so strongly that particles can overcome all forces of attraction and become a gas
  • Boiling point is higher with stronger forces of attraction between particles
  • Cooling a gas makes particles slow down and form a liquid, called condensing
• Evaporation:

  • Particles at the surface of a liquid with enough energy can break away to form a gas
  • Occurs at any temperature
  • Particles in a closed container can collide with liquid surface particles and condense back into the liquid
• Sublimation:

  • Some substances can change directly from a solid to a gas, or vice versa, without involving a liquid
  • Sublimation is solid to gas, deposition is gas to solid
  • Example: carbon dioxide sublimes at -78.5°C
• Determining physical state at a particular temperature:

  • Below melting point: solid
  • Between melting and boiling point: liquid
  • Above boiling point: gas
• Diffusion in gases:

  • Particles in gases can move freely
  • Example: ammonia gas can spread quickly in a room due to particle movement
• Diffusion is the spreading out of particles from where they are at a high concentration to where they are at a low concentration
• Diffusion occurs in gases and liquids
• Particles in a gas move faster than particles in a liquid
• Diffusion through a liquid is slow if the liquid is completely still
• The solubility of a solid in a solvent at a particular temperature is defined as 'the mass of solute which must dissolve in 100 g of solvent at that temperature to form a saturated solution'
• A saturated solution contains as much dissolved solid as possible at a particular temperature
• The solubility of sodium chloride in water at 25 °C is about 36 g per 100 g of water
• To measure the solubility of a solid in water at a specific temperature, you can follow a procedure that involves heating, stirring, cooling, and evaporating the solution
• Supersaturated solutions contain more dissolved solid than expected at a specific temperature
• Adding a tiny crystal of solid to a supersaturated solution causes all the extra solute to crystallise out, leaving a normal saturated solution
• Having undissolved solid present when making a saturated solution prevents supersaturated solutions from forming
• Solubility of potassium nitrate at 40 °C is 61.4 g per 100 g of water
• Solubility curves show how the solubility of solids changes with temperature

  • Most solids have solubility curves where solubility increases with temperature
• At 10 °C, the solubility of potassium chloride is 31.2 g per 100 g of water

  • 19.8 g of potassium chloride will crystallise out if the temperature falls to 10 °C