0
$\begingroup$

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?

$\endgroup$
1
$\begingroup$

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.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.