Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Mullins 1st Edition

Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics

Problem 18a

Chapter 4, Problem 18a

For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.
(a) Boiling water

Verified step by step guidance

Step 1: Understand the concept of entropy (∆S°). Entropy is a measure of the disorder or randomness in a system. Processes that increase disorder typically result in a positive ∆S°, while processes that decrease disorder result in a negative ∆S°.

Step 2: Analyze the physical change occurring during boiling. Boiling water involves a phase transition from liquid to gas. In the liquid phase, water molecules are relatively close together and have limited freedom of movement. In the gas phase, water molecules are widely spaced and move freely, increasing randomness.

Step 3: Compare the entropy of the liquid phase to the gas phase. The gaseous state has significantly higher entropy than the liquid state due to the increased molecular freedom and disorder.

Step 4: Determine the sign of ∆S° for the process. Since boiling water results in a transition to a more disordered state (gas), the entropy change (∆S°) is expected to be greater than 0.

Step 5: Conclude that ∆S° is positive for boiling water because the process increases the randomness and disorder of the system as water transitions from liquid to gas.

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Key Concepts

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

Entropy (∆S°)

Entropy, denoted as ∆S°, is a measure of the disorder or randomness in a system. In thermodynamics, a positive change in entropy indicates an increase in disorder, while a negative change suggests a decrease. Understanding how entropy changes during a process is crucial for predicting the spontaneity and feasibility of reactions.

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.

Molecular Freedom and Disorder

As molecules transition from a more ordered state (liquid) to a less ordered state (gas), the freedom of movement increases significantly. This increase in molecular freedom contributes to a rise in entropy, which is why boiling water is expected to have a positive ∆S° value, reflecting the greater disorder in the gaseous state.

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Related Practice

Textbook Question

For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.

(c)

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Textbook Question

For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.

(b) 2 C₆H₁₄(l) + 19 O₂(g) → 12 CO₂(g) + 14 H₂O(g)

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Textbook Question

For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.

(d)

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Textbook Question

The combustion of alkanes is exothermic (∆H° < 0) . Would you expect the combustion of butane or cyclobutane to be more exothermic?

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Textbook Question

Which conformation in each of the following pairs has the least strain energy?

(c)

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Textbook Question

Which conformation in each of the following pairs has the least strain energy?

(b)

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For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.(a) Boiling water

Verified video answer for a similar problem:

Key Concepts

Entropy (∆S°)

Phase Changes

Molecular Freedom and Disorder

For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.
(a) Boiling water