Melting & Boiling

Heating Curve of H₂O

I. Region

• Solid(ice)
• Temperature increases from -30ᴼC to 0ᴼC as thermal energy is absorbed by the ice, which results in an increase in the average KE of the ice particles.
• The particles in a solid are held together by strong bonds.
• There is no change in state.

II. Region

• A mixture of solid(ice) and liquid(water)
• The temperature remains constant at 0ᴼC during melting
• The temperature remains constant as the thermal energy is absorbed to overcome the strong bonds between particles. 
• The particles can move out of their fixed positions and hence are further apart from one another.
• Therefore there is a change of state from solid to liquid

III. Region

• Liquid(water)
• There is no change of state
• Temperature increases from 0ᴼC to 100ᴼC as thermal energy is absorbed by the water, which results in an increase in the average KE of the water molecules.
• The molecules in the liquid are held together by strong bonds.

IV. Region

• A mixture of liquid(water) and gas (steam).
• The temperature remains constant at 100ᴼC during boiling
• The temperature remains constant as thermal energy is absorbed to break the intermolecular bonds between particles,
• provide energy for particles to push back on the surrounding atmosphere and increase the average space between particles. 
• Therefore there is a change of state from liquid to gas.

V. Region

• Gas (stream)