Phase Changes

Process:

• Constant temperature: $dT=0$
• Constant pressure: $dP=0$
• Add heat: $\delta Q>0$
  $\Rightarrow$ Evaporation

Heat of Evaporation:

The necessary energy to evaporate 1kg of liquid.
$Q_{evap}=h_v-h_l$

Mixture Laws:

• Recall: Vapor Mass Fraction: $Y$
• Recall: Enthalpy: $h=(1-Y)h_l+Y{h}_v⟶dh=(h_v-h_l)dY$
• Entropy of Mixture: $s=(1-Y)s_l+Y{s}_v⟶ds=(s_v-s_l)dY$
• Entropy change: $ds=\frac{dh}{T}-\frac{v}{T}dP\to ds=\frac{h_v-h_l}{T}dY\to s_v-s_l=\frac{h_v-h_l}{T}>0$