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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=ΔHtotal=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 : ΔHtotal=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.

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Thermodynamics in Energy Engineering

Hanyang University