Indicate whether each statement is true or false: (c) Molecules that exhibit a liquid crystalline phase do so at well-defined temperatures and pressures.

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Step 1: Understand the concept of liquid crystalline phase. Liquid crystals are a state of matter that has properties between those of conventional liquids and those of solid crystals. They can flow like a liquid, but have the molecular order of a crystal.

Step 2: Consider the statement 'Molecules that exhibit a liquid crystalline phase do so at well-defined temperatures and pressures.'

Step 3: Recall that the phase of a substance (solid, liquid, gas, or liquid crystal) is determined by temperature and pressure. For a given substance, there are specific ranges of temperature and pressure at which it will exhibit a particular phase.

Step 4: Apply this knowledge to the statement. If a molecule can exhibit a liquid crystalline phase, it will do so at specific temperatures and pressures.

Step 5: Therefore, the statement 'Molecules that exhibit a liquid crystalline phase do so at well-defined temperatures and pressures.' is true.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Liquid Crystals

Liquid crystals are states of matter that have properties between those of conventional liquids and solid crystals. They can flow like a liquid but have some degree of order, particularly in their molecular arrangement. This unique phase allows them to exhibit anisotropic properties, meaning their optical and physical properties can vary based on direction.

Phase Transition

A phase transition is the transformation of a substance from one state of matter to another, such as from solid to liquid or liquid to gas. For liquid crystals, these transitions occur at specific temperatures and pressures, where the molecular arrangement changes, leading to distinct phases like nematic or smectic. Understanding these transitions is crucial for determining the conditions under which liquid crystals exhibit their unique properties.

Thermodynamic Stability

Thermodynamic stability refers to the conditions under which a substance maintains its phase without spontaneous change. For liquid crystals, this stability is influenced by temperature and pressure, which dictate the phase they occupy. At well-defined temperatures and pressures, liquid crystals can exist in a stable state, making it essential to understand these parameters when evaluating their behavior.

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Related Practice

Textbook Question

Use the phase diagram of neon to answer the following questions. (b) What can you say about the strength of the intermolecular forces in neon and argon based on the critical points of Ne and Ar (see Table 11.5.)?

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Textbook Question

At 25°C gallium is a solid with a density of 5.91 g/cm³ and a melting point, 29.8°C, just slightly above room temperature. The density of liquid gallium just above the melting point is 6.1 g/cm³. Based on this information, what unusual feature would you expect to find in the phase diagram of gallium?

Textbook Question

In all four liquid crystalline phases shown in Figure 11.32, the long axis of the molecule preferentially orders along one or more specific directions. In three of the four phases the molecules also lose some freedom of translational motion. In which of the four liquid crystalline phases do the molecules retain the freedom to move in all three directions that they possess in the liquid phase: nematic, smectic A, smectic C, or cholesteric?

Textbook Question

As the intermolecular attractive forces between molecules increase in magnitude, do you expect each of the following to increase or decrease in magnitude? (g) critical temperature.