Where do you want to go ?

What is a State ?

Gibbs Phase Rule

oF = C - P + 2

Initial State

At a given state all the properties of a system are fixed and can be measured or calculated.

Lesson 3D: page 1 of 25

I hope you recall from chapter 1 that in any given state, all of the properties of the matter inside the system boundary are fixed.
In the previous lesson, we introduced the Gibbs Phase Rule.
The Gibbs Phase Rule allows us to determine exactly how many intensive properties we must specify in order to fix, or completely specify the state of a system.
In order to use Gibbs Phase Rule, we must know what chemical species are in the system and what phases exist in the system as well.
Once we have specified a number of intensive properties equal to the number of degrees of freedom, then ALL OTHER intensive properties of the system can be determined.
If we have pure liquid water in our system, then we have 1 – 1 + 2 = 2 oFreedom.
We can specify 2 intensive variables. We usually specify T & P because they are useful and easy to measure. But we might just as well have specified the density and the specific enthalpy because these are also intensive properties.