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Chapter 11: Problem 42

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 \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(l) ?(\mathbf{b})\) 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?

Short Answer

Expert verified
The observation indicates that the specific heat of ethyl chloride in its gaseous state, \(C_{g}\), must be greater than the specific heat of ethyl chloride in its liquid state, \(C_{l}\). To calculate the final temperature of the surface, we must consider the: 1. Enthalpy of vaporization, 2. Enthalpy of heating, and 3. Enthalpy of cooling, by accounting for their respective effects on temperature.

Step by step solution

01

Analyze the Observation

The observation tells us that when liquid ethyl chloride is sprayed on a room-temperature surface, the surface cools down considerably. This indicates that the gaseous ethyl chloride has a lower temperature than the liquid ethyl chloride, which means that the heat is being transferred from the surface to the ethyl chloride.
02

Compare Specific Heat of Ethyl Chloride in Liquid and Gaseous States

From the observation, we can infer that the specific heat of ethyl chloride in its gaseous state, \(C_{g}\), must be greater than the specific heat of ethyl chloride in its liquid state, \(C_{l}\). This is because a higher specific heat allows the gaseous ethyl chloride to absorb more heat per unit mass, resulting in a significant temperature decrease on the surface.
03

Identify the Enthalpies Involved in the Process

To calculate the final temperature of the surface, we must consider the following enthalpies: 1. Enthalpy of vaporization: The heat absorbed by liquid ethyl chloride to convert into a gaseous state. 2. Enthalpy of heating: The heat absorbed by gaseous ethyl chloride to increase its temperature. 3. Enthalpy of cooling: The heat lost by the surface to cool down. These enthalpies are related to each other by the principle of conservation of energy: the heat lost by the surface must be equal to the heat gained by the ethyl chloride. To calculate the final temperature of the surface, we need to account for all these enthalpies and their respective effects on temperature.

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Most popular questions from this chapter

(a) When you exercise vigorously, you sweat. How does this help your body cool? (b) A flask of water is connected to a vacuum pump. A few moments after the pump is turned on, the water begins to boil. After a few minutes, the water begins to freeze. Explain why these processes occur.

Based on the type or types of intermolecular forces, predict the substance in each pair that has the higher boiling point: (a) propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\) or \(n\) -butane \(\left(\mathrm{C}_{4} \mathrm{H}_{10}\right),(\mathbf{b})\) diethyl ether $\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}\right)\( or 1 -butanol \)\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\right)$ (c) sulfur dioxide \(\left(\mathrm{SO}_{2}\right)\) or sulfur trioxide \(\left(\mathrm{SO}_{3}\right)\), (d) phosgene \(\left(\mathrm{Cl}_{2} \mathrm{CO}\right)\) or formaldehyde \(\left(\mathrm{H}_{2} \mathrm{CO}\right)\). Look up and compare the normal boiling points and nor-

Ethylene glycol \(\left(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}\right)\) and pentane \(\left(\mathrm{C}_{5} \mathrm{H}_{12}\right)\) are both liquids at room temperature and room pressure, and have about the same molecular weight. (a) One of these liquids is much more viscous than the other. Which one do you predict is more viscous? (b) One of these liquids has a much lower normal boiling point \(\left(36.1^{\circ} \mathrm{C}\right)\) compared to the other one \(\left(198^{\circ} \mathrm{C}\right)\). Which liquid has the lower normal boiling point? (c) One of these liquids is the major component in antifreeze in automobile engines. Which liquid would you expect to be used as antifreeze? (d) One of these liquids is used as a "blowing agent" in the manufacture of polystyrene foam because it is so volatile. Which liquid would you expect to be used as a blowing agent?

\(\mathrm{CHClF}_{2}\) is a type of hydrochlorofluorocarbon (HCFC) that has a comparatively lower damaging effect on the ozone layer. It is used as a replacement for chlorofluorocarbons (CFCs). The heat of vaporization is \(233.95 \mathrm{~kJ} / \mathrm{g}\). What mass of this substance must evaporate to freeze \(15 \mathrm{~g}\) of water initially at \(15^{\circ} \mathrm{C}\) ? (The heat of fusion of water is \(334 \mathrm{~J} / \mathrm{g} ;\) the specific heat of water is \(4.18 \mathrm{~J} / \mathrm{g} \cdot \mathrm{K} .\) )

Describe how a cholesteric liquid crystalline phase differs from a smectic A liquid crystalline phase.
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