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Chapter 11: Problem 57

(a) What is the significance of the critical point in a phase diagram? (b) Why does the line that separates the gas and liquid phases end at the critical point?

Short Answer

Expert verified
(a) In a phase diagram, the critical point is the unique temperature and pressure at which the gas and liquid phases of a substance have identical densities and become indistinguishable. It signifies the highest temperature and pressure at which a gas can be liquefied and marks the transition of a substance into a supercritical fluid that exhibits properties of both gas and liquid phases. (b) The gas-liquid phase boundary ends at the critical point because, beyond this point, the gas and liquid phases become indistinguishable and the substance exists as a supercritical fluid. Thus, it is not possible to separate the gas and liquid phases beyond the critical point.

Step by step solution

01

(a) Significance of the critical point

In a phase diagram, the critical point refers to the unique temperature and pressure at which the gas and liquid phases of a substance have identical densities and become indistinguishable from each other. This point denotes the end of the gas-liquid phase boundary and signifies the highest temperature and pressure at which a gas can be liquefied by an increase in pressure. Beyond the critical point, the substance is referred to as a supercritical fluid that exhibits properties of both gas and liquid phases. The critical point is significant as it provides information on the conditions under which a substance can transition between the gas and liquid phase.
02

(b) Gas-Liquid phase boundary ending at the critical point

The line that separates the gas and liquid phases in a phase diagram is known as the phase boundary. This boundary represents the set of conditions (temperature and pressure) under which the substance can coexist in both gas and liquid phases. The phase boundary ends at the critical point because this is the point at which the gas and liquid phases become indistinguishable from each other. Beyond the critical point, there are no distinct gas and liquid phases, and the substance exists as a supercritical fluid. As a result, it isn't possible to separate the gas and liquid phases beyond the critical point, which is why the gas-liquid phase boundary ends at this point.

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Most popular questions from this chapter

(a) When you exercise vigorously, you sweat. How does this help your body cool? (b) A flask of water is connected to a vacuum pump. A few moments after the pump is turned on, the water begins to boil. After a few minutes, the water begins to freeze. Explain why these processes occur.

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