General

• What is always conserved when a substance undergoes a change of state
• Sublimation


  When a solid changes into a gas without passing through a liquid state
• Condensation


  When a gas changes into a liquid state
• Water boils in an open pan

  Some of the water will evaporate and turn into water vapour, leaving the pan and decreasing the mass of the pan. The mass of the whole system however remains constant.
• Bathroom mirror mists up

  1. Hot water evaporates to form water vapour

  2. This water vapour lands on the cooler mirror

  3. The vapour condenses and returns to liquid state on the mirror's surface