States of Matter

Water is the ONLY substance on Earth to naturally exist in all three states (solid, liquid and gas).  Other substances can exist in these states but must be forced to do so by artificial means.

This means that the chemistry of water doesn’t change; it is still H2O but the physical form changes.  These states are liquid (water), vapour/gas (evaporation) and solid (ice, hail, snow).

 

Liquid Water

Liquid water is the form of water that most of us think of first when we here the word ‘water’.  This is the type of water that comes out of our taps and falls from the sky when it rains.  Liquid water cannot be compressed and has a very high attraction between individual molecules.  Liquid water makes up over 98% of the water on the Earth’s surface or underground with the other 1-2% being icecaps and glaciers.

 

 

Figure 1:  Liquid Water in a Stream in Australia
(Source: http://en.wikipedia.org/wiki/Stream)

 

Solid Water

Solid water is the form of water that exists as snow, sleet, hail and is generally concentrated around the two polar icecaps.  Solid water has a greater volume and is less dense.  This means that the molecules are spaced further apart than liquid water which is why icebergs float.  Glaciers and ice caps cover almost 10% of the worlds land mass.

 

 

Figure 2:  An Ice Shelf in Antarctica,
(Photo by Jo Jacka Courtesy Australian Antarctic Division © Commonwealth of Australia 2006)
(permission granted)

 

Water Vapour (Gas)

Water vapour is the gas phase of water and is produced from either:

  • Evaporation of liquid water
  • Sublimation (where water goes from a solid to a gas without becoming a liquid first) of solid water
  • Transpiration (water from the leaves of plants)

There is approximately 12,900km3 of water vapour in the atmosphere at any given time which is only 0.0008% of the total water on Earth.  Water vapour is less dense than both liquid and solid water.

 

Figure 3:  Water Vapour as Mist over an Australian Landscape
(Source: http://en.wikipedia.org/wiki/Mist)


Australian Curriculum links

Year 8

Science Understanding - Chemical sciences

(ACSSU151)  The properties of the different states of matter can be explained in terms of the motion and arrangement of particles

(ACSSU225)  Chemical change involves substances reacting to form new substances