- STATES OF MATTER:
Solid: A solid object has a definite form (shape) and a definite volume. Examples: a table, a rock, a sheet of paper, a salt crystal.
Liquid: A liquid object has a definite volume but no definite form or shape. You can pour a glass of milk into a soup bowl to make a wider shape.
You can also pour it on the ground and spread it out into a puddle.
Water, apple juice, corn oil, and alcohol are also liquid.
Gas: A gas has neither a definite form nor a definite volume. The molecules of a gas spread out to fill the available space in any container.
They can also be compressed (squeezed closer together) under pressure, and they tend to expand if you raise the temperature.
Examples of gases: the air in the room, the air in a "empty" jar, the steam above the water in a hot kettle.
Most common gases are colorless,
but chlorine gas is green and bromine is brownish-orange.
- MELTING:
The temperature at which a solid changes into a liquid (or vice versa) is called its melting point (or freezing point). The melting point of water (or ice) is 0o C.
At its melting point, a solid absorbs heat when it melts.
The amount of heat needed to melt a solid is called its heat of fusion. The heat of fusion of ice (or water) is 40 cal/g
- BOILING and EVAPORATION:
The temperature at which a liquid changes into a gas is called its boiling point. The boiling point of water is 100o C.
At its boiling point, a liquid absorbs heat as it evaporates or boils.
The amount of heat needed to boil (vaporize) a liquid is called its heat of vaporization.
Water has a very great heat of vaporization, equal to 180 cal/g, nearly the highest of any substance known.
The high heat of vaporization keeps liquid water (in ponds and oceans) from evaporating-- the water remains liquid, and very little evaporates.
Animals and other forms of life can usually live in the water without fear that it might evaporate-- this makes life possible on our planet!
This also means that any water that does evaporate cools things down a lot. For example,
when you sweat, the evaporation of the water in your sweat cools you off.
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