[Asmayus]

Hello, A question I was asked in an exam threw me and I was wondering what the answer was:

For the following phase transition:

H²0 _Solid    H²0 _Liquid

Briefly explain why the Entropy and Enthalpy are both positive.



I understand why it would be positive if it was a one way reaction, (from solid to liquid) and negative going from liquid to solid, but not why equilibrium would yield positive values. Please note that the equilibrium arrow ( ) is not used in the question, just a two headed one I approximated above. (Though I assume it means the same thing)

If you could set me straight I would appreciate it.

Cheers,
 Asmayus

Edited for clarity

[Yggdrasil]

The question likely meant for you to explain the increase of both enthalpy and entropy during the process of melting (solid --> liquid).  The double arrow is confusing, but the concept still applies.  Whenever you see a chemical reaction written, the right hand side will always be the reactants and the left hand side will always be the products regardless of the arrows used.  These conventions also define the signs on ΔH and ΔS (e.g. ΔH = H_products - H_reactants) .

[Asmayus]

Ah, I see! Thank you for the help

[Johnny010]

They are both positive because as solid->liquid entropy increases (measure of disorder).
The enthalpy is positive due to heat having to be supplied (q) to the system in order for solid->liquid.

That is a basic description of course.