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Chapter 11: Problem 41

(a) What phase change is represented by the "heat of vaporization" of a substance? (b) Is the process of vaporization endothermic or exothermic? (c) If you compare a substance's heat of vaporization to the amount of heat released during condensation, which one is generally larger (consider the numerical value only)?

Short Answer

Expert verified
(a) The "heat of vaporization" represents the phase change from a substance's liquid phase to its gaseous phase. (b) The process of vaporization is endothermic as heat energy is absorbed to overcome intermolecular forces. (c) Comparing the numerical values of the heat of vaporization and the heat released during condensation, they are equal as they are reverse processes with the same energy involved but opposite signs.

Step by step solution

01

(a) Heat of Vaporization Definition

Heat of vaporization is the amount of heat energy required to transform a substance from its liquid phase to its gaseous phase. In short, it is the energy required to vaporize a substance.
02

(b) Endothermic or Exothermic Process

During vaporization, energy is required to overcome the intermolecular forces holding molecules together in the liquid state; thus, heat energy is absorbed. This means the process of vaporization is endothermic.
03

(c) Comparison between Heat of Vaporization and Heat Released during Condensation

The heat of vaporization is the amount of energy needed for a substance to vaporize, while the heat released during condensation is the energy released when a substance condenses from its gaseous state to its liquid state. Since these processes are reverse of each other, they both have the same numerical value for energy involved, but with opposite signs. In terms of numerical values only, they are equal.

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Most popular questions from this chapter

(a) Do you expect the viscosity of glycerol, $\mathrm{C}_{3} \mathrm{H}_{5}(\mathrm{OH})_{3}$, to be larger or smaller than that of 1 -propanol, \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH} ?\) (b) Explain. [Section 11.3\(]\)

(a) Which is generally stronger, intermolecular interactions or intramolecular interactions? (b) Which of these kinds of interactions are broken when a liquid is converted to a gas?

The following data present the temperatures at which certain vapor pressures are achieved for dichloromethane $\left(\mathrm{CH}_{2} \mathrm{Cl}_{2}\right)\( and methyl iodide \)\left(\mathrm{CH}_{3} \mathrm{I}\right):$ (a) Which of the two substances is expected to have the greater dipole-dipole forces? Which is expected to have the greater dispersion forces? Based on your answers, explain why it is difficult to predict which compound would be more volatile. (b) Which compound would you expect to have the higher boiling point? Check your answer in a reference book such as the CRC Handbook of Chemistry and Physics. (c) The order of volatility of these two substances changes as the temperature is increased. What quantity must be different for the two substances for this phenomenon to occur? (d) Substantiate your answer for part (c) by drawing an appropriate graph.

It often happens that a substance possessing a smectic liquid crystalline phase just above the melting point passes into a nematic liquid crystalline phase at a higher temperature. Account for this type of behavior.

(a) Would you expect the viscosity of isopropanol, \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOH},\) to be larger or smaller than the viscosity of ethanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) ? (b) Would you expect the viscosity of isopropanol to be smaller or larger than the viscosity of 1-propanol, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{OH}$ ?
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