STATES OF MATTER
There are three states, or phases, of matter.
When a substance changes from one state, or phase, of matter to another we say that it has undergone a change of state.
The change of state from solid to liquid state is called melting.
The temperature at which the solid states of the substance changes into the liquid states of the substance is called its melting point.
The temperature remains constant until the entire amount solid is converted into liquid state
The change of state from liquid to vapour is called vaporisation.
The liquid and vapour states of the substance coexist in thermal equilibrium during the change of state from liquid to vapour.
The temperature at which the liquid states of the substance change to its vapour state is called its boiling point.
The process of changing gas (or vapour) to a liquid by cooling is called condensation
Condensation is the reverse of boiling (or vaporisation).
The process f changing a liquid into a solid by cooling is called freezing
Freezing is reverse of melting
Freezing means solidification.
SUBLIMATION AND DESPOSITION
The process of changing of solid directly into vapour (or gas) is called sublimation.
The process of changing of vapour (or gas) directly into solid is called sublimation and desposition.
EFFECT OF PRESSURE ON MELTING POINT
Under normal atmospheric pressure, ice melts at 0 °C. However, this can change if the air pressure changes.
When the two ice cubes are pressed together, the melting point is lowered.
The ice melts since its temperature (0 °C) is above the new melting point.
When the ice cubes are released, the ice freezes again at 0 °C joining the two ice cubes together.