Example 1 : supercooled water

If the system is insulated (adiabatic), -10℃ H_({2})O((l)) (supercooled liquid) will be transformed to ice + liquid H_({2})O at 0℃. Calculate fraction of ice in the final mixture.

      Basis : 1 mole of initial supercooled liquid.

• Since the system is adiabatic, Qp=ΔH_total=0.
• In calculating enthalpy changes, take the reversible path. The enthalpy change of reversible path is the same with that of the original change since enthalpy is a state function.
• Regard the process as follows.

• Adiabatic : ΔH_total=ΔH₁+ΔH₂=0

Meaning: the heat needed heating H₂(l)from-10℃ to 0℃ is
provided by solidification of xmole of H₂(l)from-10℃ to H₂(s)0℃.
The latent heat is evolved from the solidification process.