Freezing & Condensation

Cooling Curve of H₂O

I. Region

• Gas(steam)
• Temperature decreases to 100ᴼC as thermal energy is released by the steam, which results in a decrease in the average KE of the gas molecules.
• There is no change in state.

II. Region

• A mixture of gas(steam) and liquid(water)
• The temperature remains constant at 100ᴼC during condensation.
• The temperature remains constant as the thermal energy is released to form the strong bonds between molecules. 
• Therefore there is a change of state from gas to liquid

III. Region

• Liquid(water)
• There is no change of state
• Temperature decreases from 100ᴼC to 0ᴼC as thermal energy is released by the water, which results in a decrease 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 solid (ice).
• The temperature remains constant at 0ᴼC during freezing
• The temperature remains constant as thermal energy is released to form strong intermolecular bonds,
• The particles are held in fixed positions, and hence are closer to one another.
• Therefore there is a change of state from liquid to solid.

V. Region

• Solid (Ice)