Question

Which of the following statements is incorrect about the triple point?

(a) The point at which the solid, liquid and gaseous phases for a substance co-exist

(b) The triple point exists for a substance at a specific temperature and pressure

(c) The triple point exists at a single temperature and is not related with pressure

(d) The system must be closed so that no vapor can escape

The question was asked in an interview for internship.

This intriguing question comes from One Component System topic in chapter Phase Rule of Engineering Chemistry I

Answer 1

The correct answer is (c) The triple point exists at a single temperature and is not related with pressure

To explain I would say: The triple point for a pure substance occurs in a closed system at a particular temperature and pressure (i.e. one cannot be varied with the other). Hence the triple point is dependent on both the factors.