States of Matter

• There are 3 states of matter - solid, liquid and gas
• States of matter state something is at a certain temperature (solid, liquid, gas) depends on how strong the forces of attraction are between the particles of the material
• How strong forces in a state are depend in 3 things:

  • The material (structure of the substance and the type of bonds holding the particles together)
  • The temperature
  • The pressure
• You can use a model called particle theory to explain how the particles in a material behave in each of the 3 states of matter by considering each particle as a small, solid inelastic sphere
• Solids

  In solids, there are strong forces of attraction between particles, which holds them close together in fixed positions to form a very regular lattice arrangement
• Solids

  The particles don't move from their positions, so all solids keep a definite shape and volume, and don't flow like liquids
• Solids

  The particles vibrate about their positions - the hotter the solid becomes, the more they'll vibrate (causing solids to expand slightly when heated)
• Liquids

  In liquids, there's a weak force of attraction between the particles. They're randomly arranged and free to move past each other, but they tend to stick closely together
• Liquids

  Liquids have a definite volume but don't keep a definite shape, and will flow to fill the bottom of a container
• Liquids

  The particles are constantly, moving with random motion. The hotter the liquids gets, the faster they move. This causes liquids to expand slightly when heated
• Gases

  In gases, the force of attraction between the particles is very weak - they're free to move and are far apart. The particles in gases travel in straight lines
• Gases

  Gases don't keep a definite shape or volume and will always fill any container
• Gases

  The particles move constantly with random motion. The hotter the gas gets, the faster they move. Gases either expand when heated, or their pressure increases
• Particle theory is a great model for explaining the 3 states of matter, but it isn't perfect. In reality, the particles aren't solid or inelastic and they aren't spheres - they're atoms, ions or molecules
• The particle theory model doesn't show the forces between the particles, so there's no way of knowing how strong they are
• State symbols tell you the state of a substance in an equation
• Symbol equations can also include state symbols next to each substance - they tell you what physical state the reactants and products are in
• (s) - solid
• (l) - liquid
• (g) - gas
• (aq) - aqueous (dissolved in water)
• E.g. aqueous hydrochloric acid reacts with solid calcium carbonate to form aqueous calcium chloride, liquid water and carbon dioxide gas:

  2HCl(aq) + CaCO3(s) -> CaCl2(aq) + H2O(l) + CO2(g)