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Ch.19 - Free Energy & Thermodynamics
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Not the one you use?Change textbook
All textbooksTro 6th EditionCh.19 - Free Energy & ThermodynamicsProblem 87a
Chapter 19, Problem 87a

Determine the sign of ΔSsys for each process. a. water boiling

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Identify the process: Water boiling is a phase change from liquid to gas.
Understand the concept: Entropy (S) is a measure of disorder or randomness in a system.
Recognize that gases have higher entropy than liquids due to increased molecular motion and spacing.
Since water is transitioning from a liquid to a gas, the disorder of the system increases.
Conclude that the sign of \( \Delta S_{sys} \) for water boiling is positive, indicating an increase in entropy.

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Key Concepts

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

Entropy (ΔS)

Entropy, denoted as ΔS, is a measure of the disorder or randomness in a system. In thermodynamics, an increase in entropy indicates a greater degree of disorder, while a decrease suggests a more ordered state. Understanding how entropy changes during a process is crucial for predicting the spontaneity and direction of chemical reactions.
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Phase Changes

Phase changes, such as boiling, involve transitions between different states of matter (solid, liquid, gas). During boiling, water transitions from a liquid to a gas, which typically results in an increase in entropy due to the greater freedom of movement and arrangement of gas molecules compared to liquid molecules. This concept is essential for analyzing the sign of ΔS in phase transitions.
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Second Law of Thermodynamics

The Second Law of Thermodynamics states that the total entropy of an isolated system can never decrease over time. It implies that natural processes tend to move towards a state of maximum entropy. When considering processes like boiling, this law helps predict that the entropy of the system will increase, leading to a positive ΔS for the boiling of water.
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Related Practice
Textbook Question

Nitrogen dioxide, a pollutant in the atmosphere, can combine with water to form nitric acid. One of the possible reactions is shown here. Calculate ΔG° and Kp for this reaction at 25 °C and comment on the spontaneity of the reaction. 3 NO2(g) + H2O(l)→ 2 HNO3(aq) + NO(g)

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Textbook Question

Consider the reaction: 2 NO(g) + O2(g) ⇌ 2 NO2(g) The following data show the equilibrium constant for this reaction measured at several different temperatures. Use the data to find ΔH°rxn and ΔS°rxn for the reaction.

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Textbook Question

Determine the sign of ΔSsys for each process. b. water freezing

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Textbook Question

A reaction has an equilibrium constant of 8.5⨉103 at 298 K. At 755 K, the equilibrium constant is 55.2. Find ΔH°rxn for the reaction.