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Water Question


aommaster

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Are you asking why there are seperate phases? The phases properties are formed by the different interactions between the molecules. Phase changes occur at a certain corresponding pressures and temperatures. As the molecules are brought closer together by lower temperature or higher pressure, intermolecular forces and bonding occurs.

 

Gases are pretty much free of intermolecular forces as they are usually so far apart.

 

Liquids are held together by van der Waals forces (ion-dipole, dipole-dipole and London dispersion forces) and hydrogen bonding.

 

Solids can be bound by the same forces as for liquids, also by covalent bonds, ionic bonds or the delocalised electrons in metals.

 

With H2O there is lots of hydrogen bonding in the liquid phase, but in ice it forms a lattice of hydrogen with long bond lengths which is why it is less than dense than water.

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At 100oc water boils and evaporates into the air, at 100oc all the bonds are broken which link the molecules in water (l), however even below 100oc some evaporation from water surfaces occurs, with water molecules “breaking” free and escaping into the air. These water molecules that have “broken” away are named as water vapour. Water vapour enters the atmosphere by evaporation of water, i.e. lakes and rivers, water may also enter the atmosphere by transpiration from plants and trees, that’s why water vapour occurs below 100oc.

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if you watch a boiling kettle, the spout will have an area that is clear directly above it, that is Gaseous water (steam) then just above that you`ll see what`s mistakenly called Steam, in fact that`s re-condensed water vapor. Steam is invisible :)

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YT2095 said in post #8 :

if you watch a boiling kettle, the spout will have an area that is clear directly above it, that is Gaseous water (steam) then just above that you`ll see what`s mistakenly called Steam, in fact that`s re-condensed water vapor. Steam is invisible :)

 

Why can we see water vapour?

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