Phase Equilbrium

Question 1

Define state of balance (equilibrium)

Answer 1

Experiences no changes when isolated from its surroundings

Question 2

Give the gibbs phase rule for different phase and component systems

Answer 2

• Single phase single component system , F=2 - area on PT diagram
• Two phase single component system, F=1 - line on PT diagram
• Three phase single component system, F=0 - point on PT diagram (invariant)
• Two phase two component system, F=2

Question 3

Define triple point

Answer 3

all three phases can exist in equilibrium = where sublimation, fusion and vaporisation curves join = F=0

Question 4

Define critical point

Answer 4

End of vapourisation curve

Question 5

Define supercritical region

Answer 5

Above critical point

Question 6

Functions of the Phase diagram

Answer 6

PV diagram. Useful to show process paths and work terms.

PT diagram. To show three phases, triple point and critical point. 

TV diagram. For the development of entropy as a concept.

TS diagram. Allows easy visualisation of the various heat terms.

PH diagram. Particularly useful for heat engines (e.g., boiler design) 

HS diagram. To show process paths for turbines and throttles. Also called Mollier diagram.