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Chapter 11: Problem 39

Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (a) Ice-cream melts at room temperature. (b) Potato slices become crisp when fried. \((\mathbf{c})\) Droplets of water appear on the lid of a food container containing freshly baked bread. (d) You can see your own breath on a cold day.

Short Answer

Expert verified
a) Melting, endothermic. b) Vaporization, endothermic. c) Condensation, exothermic. d) Condensation, exothermic.

Step by step solution

01

a) Ice-cream melts at room temperature

When solid ice-cream absorbs heat from its surroundings and changes into a liquid state, the phase transition taking place is melting. Melting is an endothermic process, as it absorbs energy from the surroundings in the form of heat.
02

b) Potato slices become crisp when fried

When potato slices are fried, they lose their water content in the form of steam and the texture becomes crisp. The phase transition occurring here is vaporization or boiling. As the potato slices are heated up, the water in them obtains enough energy to turn into a gaseous state. Vaporization is an endothermic process, since heat energy is absorbed to turn water into steam.
03

c) Droplets of water appear on the lid of a food container containing freshly baked bread

The water droplets appearing on the lid are a result of the cooling down of water vapor present in the container filled with freshly baked bread. The phase transition taking place here is condensation. Water vapor cools down and transforms back into the liquid state as water droplets. Condensation is an exothermic process, as energy is released in the form of heat to the surroundings.
04

d) You can see your own breath on a cold day

On a cold day, the breath we exhale is warmer than the cold surrounding air. It contains water vapor which, when comes in contact with the cold air, loses its energy, and is converted into tiny water droplets, forming a mist or cloud. The phase transition happening here is condensation, similar to the previous case. As the water vapor loses heat energy to the cold surroundings while turning into tiny droplets, it is an exothermic process.

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Most popular questions from this chapter

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.

Which member in each pair has the greater dispersion forces? (a) \(\mathrm{CH}_{3} \mathrm{OH}\) or $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH},\( (b) \)\mathrm{NH}_{3}$ or \(\mathrm{N}\left(\mathrm{CH}_{3}\right)_{3}\), (c) $\mathrm{CH}_{2} \mathrm{Cl}_{2}\( or \)\mathrm{CH}_{2} \mathrm{Br}_{2}$

Rubbing alcohol is the common name for 2 -propanol (isopropanol), \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}\). (a) Draw the three-dimensional structure of the 2 -propanol molecule and predict the geometry around each carbon atom. (b) Is the 2 -propanol molecule polar or nonpolar? (c) What kinds of intermolecular attractive forces exist between the 2 -propanol molecules? (d) The isomer 1-propanol has the same molecular weight as 2 -propanol, yet 2 -propanol boils at \(82.6^{\circ} \mathrm{C}\) and 1 -propanol boils at \(97.2^{\circ} \mathrm{C}\). Explain the difference.

The smectic liquid crystalline phase can be said to be more highly ordered than the nematic phase. In what sense is this true?

Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (a) Iodine solid turns to iodine gas when it is heated. (b) Snowflakes turn into water when they fall on an open palm. (c) Droplets of water appear on grass in a cold humid morning. (d) Dry ice gradually disappears when left at room temperature for some period of time.
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