Boiling, evaporation and condensation


REVERSIBLE CHANGES


Reversible Changes:

•    Those changes which can be reversed are called reversible changes.

•    Reversible changes are temporary.

 

Examples:

Melting:

•    Melted chocolate can be changed back into solid chocolate by cooling.

•    Molten ice cream can be changed back to its solid form.

•    Thus, melting is a reversible change.

•    Melting of butter and chocolate are also reversible.

 

Freezing:

•    Freezing is a reversible change.

•    We can freeze orange juice to make ice lollies.

•    The ice lollies can be changed back into orange juice when kept at a room temperature.

 

Boiling, evaporation and condensation:

•    Boiling, evaporation and condensation are the examples of reversible changes.

•    If we could capture all the steam that is made when it is boiled in a closed container, we could turn it back into water by cooling it.

•    When this water is heated for some time, water starts to boil (liquid starts to evaporate) and steam escapes from the container.

•    Now, if we hold a lid over the container, the steam will liquefy or condense into small droplets of water on coming in contact with the cold lid.

•    This water can be cooled down and then kept in the freezer to form ice again.

•    Thus, the three physical states of water are reversible and can be changed by heating or cooling.

 

Dissolving:

•    Dissolving is an example of a reversible change.

•    When salt is mixed with water, it disappears because it dissolves in the water and becomes salty water.

•    Substances that dissolve in water are called soluble substances.

•    Substances that do not dissolve in water are called insoluble substances.