Entropy of solid, liquid, and gas at triple point of water


> 
> At the triple point of water how do the entropies of solid, 
>  liquid, and gas compare? 
> 
> 
> 


I think that either they will be equal or it will be that gas > liquid > solid.


I don't know if entropy is influenced by the fact that it will be at the triple point. Can someone please elaborate?




Triple point defines a situation of simultaneous equilibrium between the solid, the liquid and the gas phases.


For such an equilibrium, you simply write:


$$
\Delta S= \frac{\Delta H}{T}
$$


that rises from the fact that $\Delta G=0$. 


Considering water molar ($m$) enthalpies for each phase transition at $273\,K$:


$$
\Delta H\_{melting,m}=6.01\,kJ\,mol^{-1}
$$
$$
\Delta H\_{vaporisation,m}=45.05\,kJ\,mol^{-1}
$$
$$
\Delta H\_{sublimation,m}=51.06\,kJ\,mol^{-1}
$$


one realises that 


* the entropy of the gas phase is higher than the entropy of the liquid phase.
* the entropy of the liquid phase is higher than the entropy of the solid phase


In this respect the triple point has no peculiar behaviour compared to other points where a two-phase equilibrium is established.


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