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Chapter 11: Problem 67

Indicate whether each statement is true or false: (a) The liquid crystal state is another phase of matter, just like solid, liquid, and gas. (b) Liquid crystalline molecules are generally spherical in shape. (c) Molecules that exhibit a liquid crystalline phase do so at well-defined temperatures and pressures. (d) Molecules that exhibit a liquid crystalline phase show weaker-than- expected intermolecular forces. (e) Molecules containing only carbon and hydrogen are likely to form liquid crystalline phases. (f) Molecules can exhibit more than one liquid crystalline phase.

Short Answer

Expert verified
(a) True - The liquid crystal state is an intermediate phase between solid and liquid, exhibiting properties of both solids and liquids. (b) False - Liquid crystalline molecules typically have a rod-like or disc-like shape, not spherical. (c) True - Liquid crystalline phases occur under specific temperature and pressure conditions. (d) False - The intermolecular forces in liquid crystalline materials are weaker than solids but not weaker than expected. (e) False - Molecules containing only carbon and hydrogen usually do not form liquid crystalline phases. (f) True - Molecules can exhibit multiple liquid crystalline phases (mesophases) depending on the conditions.

Step by step solution

01

Statement (a)

The liquid crystal state is another phase of matter, just like solid, liquid, and gas. This statement is true. The liquid crystal state is an intermediate phase between solid and liquid, which exhibits properties of both solids (crystalline order) and liquids (flow, viscosity).
02

Statement (b)

Liquid crystalline molecules are generally spherical in shape. This statement is false. Liquid crystalline molecules typically are long and rigid with a rod-like or disc-like shape that helps them align and pack in intermediate arrangements between a solid and a liquid.
03

Statement (c)

Molecules that exhibit a liquid crystalline phase do so at well-defined temperatures and pressures. This statement is true. The formation of the liquid crystalline phase occurs under specific temperature and pressure conditions, which depend on the properties of the individual molecules and their interactions.
04

Statement (d)

Molecules that exhibit a liquid crystalline phase show weaker-than-expected intermolecular forces. This statement is actually false. The intermolecular forces in liquid crystalline materials are usually strong enough to maintain long-range order but weaker than the forces in solid crystals. So, the intermolecular forces are weaker than solids but not weaker than expected.
05

Statement (e)

Molecules containing only carbon and hydrogen are likely to form liquid crystalline phases. This statement is false. Most liquid crystalline molecules have a combination of polar and nonpolar groups (e.g., aromatic rings, ester links, and alkyl chains). Molecules consisting solely of carbon and hydrogen usually do not have the required structural features necessary for the formation of liquid crystalline phases.
06

Statement (f)

Molecules can exhibit more than one liquid crystalline phase. This statement is true. There are different types of liquid crystalline phases called mesophases, and molecules can exhibit multiple mesophases depending on the temperature and other conditions (e.g., nematic, smectic, or cholesteric phases).

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Most popular questions from this chapter

The vapor pressure of acetone \(\left(\mathrm{CH}_{3} \mathrm{COCH}_{3}\right)\) at \(19^{\circ} \mathrm{C}\) is 5.33 kPa. A 3.50-g sample of acetone is placed in a \(2.00 \mathrm{~L}\) container at \(22^{\circ} \mathrm{C}\). If the container is closed and the acetone is allowed to reach equilibrium with its vapor, how many grams of liquid acetone remain? (Assume that the vapor behaves like an ideal gas.)

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