Example Problem with Complete Solution

3C-2 : Application of the Gibbs Phase Rule to the Triple Point 2 pts
R-134a at its triple point is held in a rigid vessel. How many intensive variables can be independently specified?
Read : At the triple point, all three phases exist in equilibrium.
This is the unique aspect of the triple point and this problem.
Diagram: A diagram is not necessary for this problem.
Given: Number of chemical species present: C 1
Number of phases present at equilibrium: P 3
Find: oFree = ???
Assumptions: None.
Equations / Data / Solve:
Gibbs Phase Rule : oFree = C - P + 2 oFree = 0
NO intensive variables can be independently specified at the triple point !
This means that there is just one triple point and all of the properties of all of the phases are fixed !
The triple point is unique.
Verify: No assumptions were made in the solution of this problem.
Answers : oFree 0