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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, (b) False, (c) True, (d) False, (e) False, (f) True

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 \(True\). Liquid crystals are considered the fourth state of matter, distinct from solids, liquids, and gases.
02

Statement (b)

Liquid crystalline molecules are generally spherical in shape. This statement is \(False\). Liquid crystalline molecules are generally elongated and anisotropic (having properties that differ in different directions) rather than spherical in shape. This is a key feature that allows them to exhibit liquid crystal properties.
03

Statement (c)

Molecules that exhibit a liquid crystalline phase do so at well-defined temperatures and pressures. This statement is \(True\). Liquid crystalline phases have specific temperature and pressure ranges in which they occur, typically between the solid phase and the isotropic liquid phase.
04

Statement (d)

Molecules that exhibit a liquid crystalline phase show weaker-than-expected intermolecular forces. This statement is \(False\). Molecules in the liquid crystalline phase show stronger, rather than weaker, intermolecular forces. These forces help to maintain the ordered arrangement of molecules in the liquid crystalline phase.
05

Statement (e)

Molecules containing only carbon and hydrogen are likely to form liquid crystalline phases. This statement is \(False\). While it is possible for molecules containing only carbon and hydrogen (hydrocarbons) to form liquid crystalline phases, most liquid crystalline materials contain additional elements, such as nitrogen, oxygen, or halogens. This additional molecular complexity allows for the unique properties of liquid crystals.
06

Statement (f)

Molecules can exhibit more than one liquid crystalline phase. This statement is \(True\). Some molecules can exhibit several distinct liquid crystalline phases, which differ in terms of their molecular orientation, order, and symmetry. These different phases are typically observed as a function of temperature, with transitions occurring at specific temperature ranges.

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Most popular questions from this chapter

The vapor pressure of ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) at \(19^{\circ} \mathrm{C}\) is 40.0 torr. \(\mathrm{A} 1.00\) -g sample of ethanol is placed in a 2.00 \(\mathrm{L}\) container at \(19^{\circ} \mathrm{C}\) . If the container is closed and the ethanol is allowed to reach equilibrium with its vapor, how many grams of liquid ethanol remain?

One of the attractive features of ionic liquids is their low vapor pressure, which in turn tends to make them nonflammable. Why do you think ionic liquids have lower vapor pressures than most room-temperature molecular liquids?

Rationalize the difference in boiling points in each pair: (a) HF \(\left(20^{\circ} \mathrm{C}\right)\) and \(\mathrm{HCl}\left(-85^{\circ} \mathrm{C}\right),\) (b) CHCl \(_{3}\left(61^{\circ} \mathrm{C}\right)\) and \(\mathrm{CHBr}_{3}\left(150^{\circ} \mathrm{C}\right),(\mathbf{c}) \mathrm{Br}_{2}\left(59^{\circ} \mathrm{C}\right)\) and \(\mathrm{ICl}\left(97^{\circ} \mathrm{C}\right)\)

Based on their composition and structure, list \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3},\) and \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) in order of \((\mathbf{a})\) increasing intermolecular forces, (\mathbf{b} ) increasing viscosity , ( c ) increasing surface tension.

As the intermolecular attractive forces between molecules increase in magnitude, do you expect each of the following to increase or decrease in magnitude? (a) Vapor pressure, (b) heat of vaporization, (c) boiling point, (d) freezing point, (e) viscosity, (f) surface tension, ( g) critical temperature.
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