Example 1 : supercooled water
If the system is insulated (adiabatic), -10℃ HO (supercooled liquid) will be transformed to ice + liquid HO 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.