Thermal Effects

• Solids have a fixed shape and fixed volume
• liquid has a fixed volume and no fixed shape
• gas has no fixed shape and no fixed volume
• solid -> gas = endothermic
• gas -> solid = exothermic
• endothermic requires heat to be absorbed
• exothermic requires heat to be lost
• • In a solid:
  • The molecules are very close together and arranged in a regular pattern
  • The molecules vibrate about fixed positions
• • In a liquid:
  • The molecules are still close together (no gaps) but are no longer arranged in a regular pattern
  • The molecules are able to slide past each other
• In a gas:

  • The molecules are widely separated - about 10 times further apart in each direction
  • The molecules move about randomly at high speeds
• solids have a regular lattice and have very strong forces of attraction
• gas have irregular lattice and have little or no forces of attration
• absolute zero is -273℃
• liquids have irregular lattice and strong forces of attraction
• internal energy = sum of KE and PE of particles