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Ch.11 - Liquids and Intermolecular Forces
All textbooksBrown 14th EditionCh.11 - Liquids and Intermolecular ForcesProblem 39
Chapter 11, Problem 39

Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (a) When ice is heated, it turns to water. (b) Wet clothes dry on a warm summer day. (c) Frost appears on a window on a cold winter day. (d) Droplets of water appear on a cold glass of lemonade.

Verified step by step guidance
1
(a) Identify the phase transition: Ice turning to water is a transition from solid to liquid, known as melting. Determine if it is exothermic or endothermic: Melting requires energy to break the bonds in the solid structure, so it is an endothermic process.
(b) Identify the phase transition: Wet clothes drying involves the transition from liquid to gas, known as evaporation. Determine if it is exothermic or endothermic: Evaporation requires energy to overcome the intermolecular forces in the liquid, making it an endothermic process.
(c) Identify the phase transition: Frost appearing on a window involves the transition from gas to solid, known as deposition. Determine if it is exothermic or endothermic: Deposition releases energy as the gas molecules form a solid structure, so it is an exothermic process.
(d) Identify the phase transition: Droplets of water appearing on a cold glass involves the transition from gas to liquid, known as condensation. Determine if it is exothermic or endothermic: Condensation releases energy as the gas molecules form a liquid, making it an exothermic process.
Summarize the phase transitions and their energy changes: (a) Melting is endothermic, (b) Evaporation is endothermic, (c) Deposition is exothermic, (d) Condensation is exothermic.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Phase Transitions

Phase transitions refer to the changes between different states of matter, such as solid, liquid, and gas. These transitions occur when energy is added or removed from a substance, leading to changes in temperature and pressure. Common phase transitions include melting, freezing, evaporation, condensation, sublimation, and deposition.
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Phase Changes in Diagrams

Exothermic and Endothermic Processes

Exothermic processes release energy, usually in the form of heat, to the surroundings, while endothermic processes absorb energy from the surroundings. For example, melting ice (endothermic) requires heat, whereas freezing water (exothermic) releases heat. Understanding these concepts is crucial for determining the energy changes associated with phase transitions.
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Endothermic & Exothermic Reactions Example 2

Humidity and Evaporation

Humidity refers to the amount of water vapor present in the air. When wet clothes dry, the water molecules in the fabric gain enough energy to evaporate into the air, a process that requires heat (endothermic). This concept is essential for understanding how moisture is removed from surfaces and the role of temperature in evaporation.
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Related Practice
Textbook Question

Liquids can interact with flat surfaces just as they can with capillary tubes; the cohesive forces within the liquid can be stronger or weaker than the adhesive forces between liquid and surface:

(b) Which of these diagrams, i or ii, rep- resents what happens when water is on a nonpolar surface?

Textbook Question
The boiling points, surface tensions, and viscosities of water and several alcohols are as shown below: (b) How do you explain the fact that propanol and ethylene glycol have similar molecular weights (60 versus 62 amu), yet the viscosity of ethylene glycol is more than 10 times larger than propa- nol?
Textbook Question

Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (c) Rubbing alcohol in an open container slowly disappears.

Textbook Question

Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (d) Molten lava from a volcano turns into solid rock.