Ch.11 - Liquids and Intermolecular Forces

Brown - Chemistry: The Central Science 15th Edition

Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Not the one you use?Change textbook

Brown 15th Edition

Ch.11 - Liquids and Intermolecular Forces

Problem 42d

Chapter 11, Problem 42d

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.

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1. Identify the initial and final states of the substance. In this case, the initial state is molten lava (liquid) and the final state is solid rock (solid).

2. Determine the phase transition based on the change in state. The transition from a liquid to a solid is called 'freezing' or 'solidification'.

3. Determine whether the process is exothermic or endothermic. In a freezing process, heat is released as the substance changes from a higher energy state (liquid) to a lower energy state (solid). Therefore, this process is exothermic.

4. Summarize the information: The phase transition of molten lava from a volcano turning into solid rock is called freezing or solidification, and it is an exothermic process.

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Key Concepts

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

Phase Transition

A phase transition refers to the transformation of a substance from one state of matter to another, such as solid, liquid, or gas. Common examples include melting (solid to liquid) and freezing (liquid to solid). Understanding these transitions is crucial for analyzing changes in physical properties and energy exchanges during the process.

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. The classification of a phase transition as exothermic or endothermic depends on whether energy is released or absorbed during the transition. For instance, freezing is exothermic as it releases heat.

Freezing of Lava

When molten lava cools and solidifies into rock, it undergoes a phase transition known as freezing. This process is exothermic because the lava releases heat to the environment as it transitions from a liquid state to a solid state. Understanding this transition helps in grasping the geological processes involved in volcanic activity.

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Related Practice

Textbook Question

The boiling points, surface tensions, and viscosities of water and several alcohols are listed in the following table:

b. How do you explain the fact that propanol and ethylene glycol have similar molecular weights (60 vs. 62 amu), yet the viscosity of ethylene glycol is more than 10 times larger than propanol?

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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.

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Textbook Question

Ethyl chloride (C₂H₅Cl) boils at 12 °C. When liquid C₂H₅Cl under pressure is sprayed on a room-temperature (25 °C) surface in air, the surface is cooled considerably. (a) What does this observation tell us about the specific heat of C₂H₅Cl(g) as compared with that of C₂H₅Cl(l)?

Ethyl chloride (C₂H₅Cl) boils at 12 °C. When liquid C₂H₅Cl under pressure is sprayed on a room-temperature (25 °C) surface in air, the surface is cooled considerably. (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?

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