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Chapter 10: Problem 17

Use the kinetic molecular theory to explain why a liquid gets cooler as it evaporates from an insulated container.

Short Answer

Expert verified
Evaporation cools a liquid in an insulated container because the process preferentially removes molecules with higher kinetic energy, leaving behind those with lower kinetic energy. According to the Kinetic Molecular Theory, the temperature of a substance is proportional to the average kinetic energy of its molecules. Thus, as the average kinetic energy decreases due to evaporation, the temperature of the remaining liquid also decreases, causing it to get cooler.

Step by step solution

01

Understand the evaporation process

Evaporation is the process by which molecules in a liquid state turn into a gas state. For a molecule to escape the liquid and become a gas, it must have enough kinetic energy to overcome the attractive forces between it and the surrounding liquid molecules. Molecules with higher kinetic energy are more likely to evaporate.
02

Explain the effects of evaporation on the remaining liquid molecules

As the molecules with higher kinetic energy evaporate, the average kinetic energy of the remaining liquid molecules decreases. This is because the faster-moving molecules (ones with more kinetic energy) are the ones that are most likely to escape the liquid phase, leaving behind slower-moving molecules with less kinetic energy.
03

Relate the change in average kinetic energy to temperature

According to the Kinetic Molecular Theory, the temperature of a substance is proportional to the average kinetic energy of its molecules. As the remaining liquid molecules have a lower average kinetic energy after evaporation, the temperature of the liquid also decreases.
04

Discuss the role of an insulated container

The insulated container minimizes heat exchange between the liquid inside and the surrounding environment. As a result, any temperature change within the liquid is primarily due to the evaporation process rather than external factors such as heat being conducted in from the container's surroundings. This allows us to attribute the cooling of the liquid predominantly to the evaporation process.
05

Conclusion

Based on the Kinetic Molecular Theory, when a liquid evaporates from an insulated container, the liquid gets cooler because the molecules with higher kinetic energy are more likely to escape, leading to a decrease in the average kinetic energy of the remaining liquid molecules. This decrease in average kinetic energy corresponds to a decrease in temperature, thus causing the remaining liquid to become cooler.

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Most popular questions from this chapter

Why does water evaporate?

Pyrolusite is a mineral containing manganese ions and oxide ions. Its structure can best be described as a body-centered cubic array of manganese ions with two oxide ions inside the unit cell and two oxide ions each on two faces of the cubic unit cell. What is the charge on the manganese ions in pyrolusite?

In each of the following groups of substances, pick the one that has the given property. Justify each answer. a. highest boiling point: \(\mathrm{CCl}_{4}, \mathrm{CF}_{4}, \mathrm{CBr}_{4}\) b. lowest freezing point: \(\mathrm{LiF}, \mathrm{F}_{2}, \mathrm{HCl}\) c. smallest vapor pressure at \(25^{\circ} \mathrm{C}: \mathrm{CH}_{3} \mathrm{OCH}_{3}, \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\), \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\) d. greatest viscosity: \(\mathrm{H}_{2} \mathrm{~S}, \mathrm{HF}, \mathrm{H}_{2} \mathrm{O}_{2}\) e. greatest heat of vaporization: \(\mathrm{H}_{2} \mathrm{CO}, \mathrm{CH}_{3} \mathrm{CH}_{3}, \mathrm{CH}_{4}\) f. smallest enthalpy of fusion: \(\mathrm{I}_{2}, \overline{\mathrm{CsBr}, \mathrm{CaO}}\)

An ice cube tray contains enough water at \(22.0^{\circ} \mathrm{C}\) to make 18 ice cubes that each has a mass of \(30.0 \mathrm{~g}\). The tray is placed in a freezer that uses \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\) as a refrigerant. The heat of vaporization of \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\) is \(158 \mathrm{~J} / \mathrm{g}\). What mass of \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\) must be vaporized in the refrigeration cycle to convert all the water at \(22.0^{\circ} \mathrm{C}\) to ice at \(-5.0^{\circ} \mathrm{C}\) ? The heat capacities for \(\mathrm{H}_{2} \mathrm{O}(s)\) and \(\mathrm{H}_{2} \mathrm{O}(l)\) are \(2.03 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\) and \(4.18 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\), respectively, and the enthalpy of fusion for ice is \(6.02 \mathrm{~kJ} / \mathrm{mol}\).

Atoms are assumed to touch in closest packed structures, yet every closest packed unit cell contains a significant amount of empty space. Why?
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