Question

What are the limits of phase rule?

(a) Cannot determine the presence of more the one phase in a system

(b) Cannot determine solubility

(c) Cannot determine composition

(d) Can determine temperature

This question was posed to me in final exam.

This intriguing question comes from Uses and Limitations of Phase Rule in section Phase Rule of Engineering Chemistry I

Answer 1

Right choice is (a) Cannot determine the presence of more the one phase in a system

Easiest explanation: Since phase rule focusses only on one equilibrium state of the system, the presence of even tiny traces of multiple phases cannot be identified using phase rule which is the main drawback of this rule. This drawback is solved by Lever rule.