Changing its temperature can change matter from one form to
another form. If you freeze water, which is in a liquid state, it changes into a
solid state (ice). If you boil the liquid, you see the liquid escaping in the
form of bubbles and changing into a gaseous state. These states of matter are
only the physical properties. There is no change in its chemical composition.
Ice and water vapor continue to be water in different forms or states.
Sometimes a liquid can be sitting there and its molecules
will become a gas. That is called Evaporation. You might be wondering how that
can happen when the temperature is low. It turns out that all liquids can
evaporate at room temperature and pressure. Evaporation takes place when there are atoms
or molecules escaping from the liquid and turning into a vapor.
Water is a good example for evaporation and melting. Water is
transferred from the surface to the atmosphere through evaporation; the process
by which water changes from a liquid to a gas. Evaporation is the process
whereby atoms or molecules in a liquid state (or solid state if the substance
sublimes) gain sufficient energy to enter the gaseous state.
Water in the liquid state changes to water in a gaseous
state. Water evaporates to turn into water vapor. Water can evaporate or
disappear with the help of heat. Changes in temperature can increase or decrease
the rate of evaporation. Evaporate means to disappear. Water can evaporate from
soil. It evaporates off wet clothes hanging on a clothesline. Plants release
water vapor into the air. We breathe out water vapor along with carbon dioxide.
Melting : When you drop an ice cube into any liquid, it begins
to melt because the temperature of the liquid is higher than that of the ice cube. It is like
putting a snowman on your front lawn in July. You need some energy to melt ice
cube into a liquid.
Atoms in a liquid have more energy than the atoms in a solid.
The easiest energy available around is probably heat. Every substance has a certain
temperature at which it melts. It is called as its melting point. When a solid
reaches the temperature of its melting point, it changes to a liquid. For water
the temperature has to be a little over zero degrees Celsius. For salt, sugar,
or wood, the melting point would be higher than water. |
