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Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium
All textbooksMcMurry 8th EditionCh.18 - Thermodynamics: Entropy, Free Energy & EquilibriumProblem 69
Chapter 18, Problem 69

An isolated system is one that exchanges neither matter nor energy with the surroundings. What is the entropy criterion for spontaneous change in an isolated system? Give an example of a spontaneous process in an isolated system.

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Understand the concept of an isolated system: An isolated system is a thermodynamic system that does not exchange energy or matter with its surroundings. This means that any changes occurring within the system are solely due to internal processes.
Learn about entropy: Entropy is a measure of the disorder or randomness in a system. In thermodynamics, the second law states that the total entropy of an isolated system can never decrease over time.
Identify the entropy criterion for spontaneous change: For a process to be spontaneous in an isolated system, the entropy of the system must increase. This is because spontaneous processes are those that occur naturally without external influence, and according to the second law of thermodynamics, they must lead to an increase in entropy.
Apply the criterion to an example: Consider the melting of ice in a thermally insulated container (an isolated system). Initially, the system has ice at a low entropy state. As the ice melts, it turns into water, which has higher entropy due to the increased molecular disorder and movement. Thus, the entropy of the system increases, making the melting of ice a spontaneous process in this isolated system.
Summarize the concept: In summary, the entropy criterion for a spontaneous change in an isolated system is that the total entropy of the system must increase. This criterion helps predict whether a process will occur spontaneously without external intervention.

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Key Concepts

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

Entropy

Entropy is a measure of the disorder or randomness in a system. In thermodynamics, it quantifies the amount of energy in a physical system that is not available to do work. The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time, which implies that spontaneous processes tend to increase the overall entropy of the system.
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Spontaneous Processes

A spontaneous process is a reaction or change that occurs without the need for external energy input. In an isolated system, these processes are driven by the natural tendency of systems to move towards a state of higher entropy. Examples include the melting of ice at room temperature or the diffusion of a gas in a vacuum, both of which occur naturally and increase the system's entropy.
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Isolated Systems

An isolated system is one that does not exchange matter or energy with its surroundings. This means that the total energy and mass within the system remain constant over time. In the context of thermodynamics, isolated systems are important for studying the principles of energy conservation and entropy, as they provide a controlled environment to observe spontaneous changes without external influences.
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Related Practice
Textbook Question
What is the entropy change when the volume of 1.6 g of O2 increases from 2.5 L to 3.5 L at a constant temperature of 75 °C? Assume that O2 behaves as an ideal gas.
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Textbook Question
Make a rough, qualitative plot of the standard molar entropy versus temperature for methane from 0 K to 298 K. Incorporate the following data into your plot: mp = -182 °C; bp = -164 °C; °S = 186.2 J/(K*mol) at 25 °C.
Textbook Question
Give an equation that relates the entropy change in the surroundings to the enthalpy change in the system. What is the sign of ∆Ssurr for the following?(a) An exothermic reaction(b) An endothermic reaction
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What are the values of x and y for the following reaction if E° = 0.91 V and ∆G° = -527 kJ?
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Reduction of mercury(II) oxide with zinc gives metallic mercury: (b) Estimate at what temperature, if any, the reaction will become nonspontaneous