Question

In the phase diagram of a one-component system, which of the following statements is correct? (a) eutectic point (b) congruent point (c) triple point (d) critical point

Short answer

The correct answer is: Triple Point, as it's the unique set of conditions at which all three phases of a substance coexist in thermodynamic equilibrium, which fits the description of points in a phase diagram of a one-component system.

Step-by-step solution

Understanding Eutectic Point

A eutectic point in a phase diagram is the point that represents the lowest possible melting point for a mixture. However, it is typically a term used in multi-component systems, not a single component system.

Understanding Congruent Point

A congruent point in a phase diagram is the point where a solid phase changes directly into a vapor without passing through a liquid phase. But this term is not usually used in phase diagrams of a one-component system.

Understanding Triple Point

The triple point in a phase diagram is the unique set of conditions at which all three phases (solid, liquid, and gas) of a substance coexist in thermodynamic equilibrium. This term is indeed used in one-component systems.

Understanding Critical Point

The critical point is the point at which the liquid and gaseous phases of a substance become indistinguishable from one another. They merge into a single phase referred to as supercritical. However, this does not correspond to the definitions provided in this exercise.

Key concepts

Phase Diagram

A phase diagram is a graphical representation that shows the conditions under which distinct phases (like solid, liquid, and gas) occur and coexist at equilibrium. These diagrams map out pressure and temperature on the axes, providing valuable information about the stability and transitions of different phases of a substance. Phase diagrams are crucial in chemistry, physics, and material science.

For a one-component system, the phase diagram is simpler than multi-component systems, containing fewer phases and simpler transitions. The phase diagram displays boundaries called phase boundaries that separate different phases. Crossing a boundary leads to a phase transition, such as from liquid to gas, or solid to liquid.

• The triple point marks the unique condition where all three phases coexist.
• The critical point denotes the temperature and pressure at which the properties of liquid and gas phases become identical, leading to a supercritical fluid.

Understanding these points helps explain why substances behave differently under various environmental conditions.

One-Component System

A one-component system refers to a system that involves a single pure substance and its different phases. This simplifies the phase diagram since it only involves the transitions between solid, liquid, and gas phases without the complexity of mixtures or solutions.

A typical example is the water system, where water can exist in solid (ice), liquid (water), or gaseous (vapor) forms. These one-component phase diagrams effectively illustrate critical points and triple points that are essential for understanding the physical behavior and thermodynamic properties of substances.

• At the triple point of a one-component system, all three phases coexist in equilibrium.
• The critical point provides insight into the relationship between temperature and pressure for phase transitions.

This makes the study of one-component systems an important foundation in thermodynamics.

Thermodynamic Equilibrium

Thermodynamic equilibrium is a state where a system's macroscopic properties remain constant over time because it is in a steady condition. In this state, there are no net flows of matter or energy.

In the context of a one-component phase diagram, the triple point is particularly important because it's the point where solid, liquid, and gaseous phases exist together in equilibrium. This implies that at the triple point, the temperature and pressure conditions are just right to allow the three phases to coexist without any phase being favored over another.

• Thermodynamic equilibrium in a phase diagram means no phase changes occur spontaneously.
• The system's energy is optimally distributed among the phases.

Understanding thermodynamic equilibrium helps predict how a substance will react to changes in environmental conditions, such as pressure or temperature.