A: (solid state at any temperature below its melting point) Particles are very closely packed together in an orderly manner. Forces between the particles are very strong and can only vibrate at a fixed position.
A-B: As it is heated, heat energy is converted to kinetic energy. Kinetic energy increases and the molecules vibrate faster about their fixed positions, and the temperature increases.
B: (still solid) Melting has begun. Temperature remains the same, which is called the melting point. Solid begins to change into liquid.
B-C: (exists in both solid and liquid state) The temperature remains constant because the heat that is supplied to it is used to overcome the forces of attraction that hold the particles together. The heat energy that absorbed to overcome intermolecular forces is called the latent heat of fusion.
C: All has completely melted. Solid has turned into liquid.
C-D: As the liquid is heated, the molecules gain more heat energy and the temperature increase. The particles move faster because their kinetic energy is increasing. (in liquid state)
D: (still in liquid state) Molecules have received enough energy to overcome the forces of attraction between the particles. Some of the molecules start to move freely and liquid begin to change into gas.
D-E: (exists in both liquid and gaseous states) Temperature remains unchanged. The heat energy absorbed is used to overcome the intermolecular forces between the particles of the liquid rather than increase the temperature. This constant temperature is the boiling point.
E: All liquids have turned into gas.
E-F: The gas particles continue to absorb more energy and move faster. Temperature increases.
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