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Chapter 11: Problem 69

For a given substance, the liquid crystalline phase tends to be more viscous than the liquid phase. Why?

Short Answer

Expert verified
The liquid crystalline phase tends to be more viscous than the liquid phase because of the increased molecular order in the liquid crystalline phase. In this phase, the molecules exhibit some degree of long-range order, typically forming layered or aligned structures, which restricts their freedom of movement and makes it harder for them to slide past each other. This results in stronger intermolecular forces and reduced mobility, leading to higher viscosity compared to the liquid phase, where molecules are randomly arranged and can easily slide past one another.

Step by step solution

01

Definition of Liquid and Liquid Crystalline Phase

A liquid is a state of matter characterized by its ability to flow and adapt to the shape of its container, with short-range molecular order but no long-range order. On the other hand, a liquid crystalline phase is an intermediate phase between a liquid and a crystal, where the molecules exhibit some degree of long-range order while still maintaining fluidity.
02

Definition of Viscosity

Viscosity (\(\eta\)) is a measure of a fluid's resistance to flow, or deformation by shear stress or tensile stress. It refers to the internal friction between adjacent layers of fluid that are moving at different velocities. Higher viscosity means that a fluid has more resistance to flow and appears thicker. Conversely, lower viscosity indicates a thinner fluid that flows more easily.
03

Molecular Structure in Liquid and Liquid Crystalline Phase

In the liquid phase, the molecules are randomly arranged and can easily slide past one another, which allows the liquid to flow easily. In the liquid crystalline phase, the molecules are more ordered, typically forming layered or aligned structures. These ordered structures reduce the freedom of movement of the molecules, making it harder for them to slide past each other.
04

Comparing Viscosity in Liquid and Liquid Crystalline Phase

Due to the increased molecular order in the liquid crystalline phase, the molecules experience more resistance to flow. This results in a higher viscosity in the liquid crystalline phase compared to the liquid phase. The ordered molecular arrangements in the liquid crystalline phase create stronger intermolecular forces and reduce the mobility of the molecules, thus increasing the viscosity.

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Most popular questions from this chapter

(a) Which type of intermolecular attractive force operates between all molecules? (b) Which type of intermolecular attractive force operates only between polar molecules? (c) Which type of intermolecular attractive force operates only between the hydrogen atom of a polar bond and a nearby small electronegative atom?

Ethyl chloride \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}\right)\) boils at \(12^{\circ} \mathrm{C}\) . When liquid \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}\) under pressure is sprayed on a room-temperature \(\left(25^{\circ} \mathrm{C}\right)\) surface in air, the surface is cooled considerably. (a) What does this observation tell us about the specific heat of \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(g)\) as compared with that of \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(l) ?\) Assume that the heat lost by the surface is gained by ethyl chloride. What enthalpies must you consider if you were to calculate the final temperature of the surface?

Appendix \(\mathrm{B}\) lists the vapor pressure of water at various external pressures. (a) Plot the data in Appendix B, vaporpressure (torr) versus temperature \(\left(^{\circ} \mathrm{C}\right) .\) From your plot, estimate the vapor pressure of water at body temperature, \(37^{\circ} \mathrm{C}\) (b) Explain the significance of the data point at 760.0 torr, \(100^{\circ} \mathrm{C}\) (c) A city at an altitude of 5000 \(\mathrm{ft}\)above sea level has a barometric pressure of 633 torr. To what temperature would you have to heat water to boil it in this city? (d) A city at an altitude of 500 ft below sea level would have a barometric pressure of 774 torr. To what temperature would you have to heat water to boil it in this city?

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?

A watch with a liquid crystal display (LCD) does not function properly when it is exposed to low temperatures during a trip to Antarctica. Explain why the LCD might not function well at low temperature.
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