Question

A certain substance, X, has a triple-point temperature of 20°C at a pressure of 2.0 atm.

Which one of the following statements cannot possibly be true?

A) X can exist as a liquid above 20°C.

B) X can exist as a solid above 20°C.

C) Liquid X can exist as a stable phase at 25°C, 1 atm.

D) Both liquid and solid X have the same vapor pressure at 20°C.

E) All of these statements could be true

Answer 1

Answer: The statement which could possibly not be true is C -" Liquid X can exist as a stable phase at 25°C, 1atm."

Explanation:

Triple point is the point where a substance co-exist as solid liquid and gas. At any point other than the triple point, the substance exist as a single phase substance.

As shown in the diagram, Liquid cannot exist as a stable phase at 1atm( below the the triple point pressure of 2atm) as the liquid can only exist beyond the pressure of triple point.