GED Science Practice Test: Phase Changes in Matter

With an increase or decrease of energy in a system, a material in one state of matter can change to another state of matter.  The following image shows the different phase changes.  Going left to right, energy increases.  Going right to left, energy decreases:

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The different phase changes can be described as follows:

  • Melting – The process by which a substance changes from its solid state to its liquid state.
  • Freezing– The process by which a substance changes from its liquid state into its solid state.
  • Evaporation – A process by which a substance changes from its liquid state to its gas state by random particle movement.
  • Sublimation– The process by which a substance changes directly from its solid state to its gas state without becoming a liquid first.
  • Boiling– A process by which a substance changes from its liquid state to its gas state.
  • Condensation – The process by which a gas becomes a liquid.
  • Deposition-The process by which a gas changes directly from its gaseous state to its solid state without becoming a liquid first.

The point at which a substance changes from one state to another is called a point, such as the melting point.  The melting point of solid ice, for example is 32°F (or 0°C).  The different points (melting point, boiling point, etc.) are also examples of intrinsic properties.

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