Physical Chemistry : Other Phase Interface Principles

Study concepts, example questions & explanations for Physical Chemistry

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Example Questions

Example Question #1 : Other Phase Interface Principles

Which of the follow are false?

I. Three phases can coexist at the triple point.

II. It is not possible for ice to transition directly to water vapor without become a liquid first.

III. The slope of the ice/water phase curve is positive

IV. Distinct phases are not achievable above the critical point

Possible Answers:

II and IV

I only

II and III

III and IV

IV only

Correct answer:

II and III


Condition I is true. The only place three phases can coexist is at the triple point.

Condition II is false. Water in fact can undergo deposition and move from the solid phase to the gas phase directly. This occurs at pressures below 0.006atm.

Condition III is false. A peculiar fact of the water phase diagram is the slope of the solid/liquid line. For most phase diagrams, the slope is sharply positive, but that of water is negative.

Condition IV is true. No distinct phases exist above the critical point. 

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