Difficulty: Medium

Average Score: 73%

The triple point of a substance is the temperature and pressure at which of the substance exists as which of the following?

What is the triple point of a substance?

Rationale

Simultaneously in solid, liquid, and gas phases.

The triple point of a substance is a specific combination of temperature and pressure at which the three phases—solid, liquid, and gas—can coexist in thermodynamic equilibrium. This unique state is crucial for defining the properties of the substance in phase diagrams and various scientific applications.

A (Simultaneously in solid, liquid, and gas phases.) CORRECT

This choice accurately describes the triple point, where all three phases of a substance are present and stable. At this specific temperature and pressure, the solid, liquid, and vapor phases exist together, allowing for unique physical phenomena and measurements.

B (As soil with gas and solid trapped in liquid.) YOUR ANSWER

This option misrepresents the concept of the triple point. Soil is a complex mixture that does not represent a pure substance's phase equilibrium. The triple point concerns pure substances and their phases, not mixtures where solid and gas are contained within a liquid medium.

C (As a gel with solid and liquid trapped in gas.) YOUR ANSWER

This choice introduces the concept of a gel, which is not relevant to the definition of a triple point. A gel is a colloidal system, and the phases of matter in a gel do not include the simultaneous presence of solid, liquid, and gas in equilibrium, as required by the definition of the triple point.

D (Simultaneously in solid, gel, and plasma phases.) YOUR ANSWER

This option incorrectly includes gel and plasma phases. While the triple point involves solid, liquid, and gas phases, gel and plasma are not phases that coexist at the triple point of a substance. Plasma represents a state of matter that occurs at much higher energy levels, while a gel is a specific colloidal phase that does not fit within the classical definitions of states of matter relevant to the triple point.

Conclusion

The triple point of a substance is a critical concept in thermodynamics, where it is defined as the unique set of conditions under which solid, liquid, and gas phases coexist in equilibrium. Understanding this phenomenon is essential for applications in various scientific fields, particularly in studying phase transitions and material properties. Options B, C, and D fail to correctly represent the fundamental definition of a triple point, which is anchored in the simultaneous presence of the three classical phases of matter.

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