What is a maxwell construction.?

[misslondonuk]

what is a maxwell construction...?

What is a maxwell construction when applied to van der Waals isotherms??

please help, i really don't understand it.

Thanks in advance

 

[nbo10]

For lack of a quicker reference http://en.wikipedia.org/wiki/Maxwell_relations

 

[DrDu]

The Maxwell isotherm is based on the assumption that the system is spatially homogeneous. However, there are regions of the isotherm which are unstable and tend to segregate into fluid and gaseous phases. The Maxwell construction is a method to determine the phase equilibrium in the inhomogeneous region.
It is not related to the Maxwell relations in contrast to the answer of nbo10.

 

[genneth]

To expand on DrDu's excellent answer, in phase equilibrium, we need the chemical potential of the liquid and gas phases to be equal. In particular, since $$d\mu = -s dT + v dp$$, to have equal $$\mu$$ at equal temperature requires the integral of v dp to be zero, i.e. the signed area under the curve to be zero. We arrange for this by making the opposing areas equal.