Ch.19 - Chemical Thermodynamics

Brown - Chemistry: The Central Science 15th Edition

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Brown 15th Edition

Ch.19 - Chemical Thermodynamics

Problema 34a

Capitolo 19, Problema 34a

(a) In a chemical reaction, two gases combine to form a solid. What do you expect for the sign of ΔS?

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Identify the phase changes in the reaction. In this case, two gases combine to form a solid.

Recall that entropy (ΔS) is a measure of the randomness or disorder of a system. Gases have higher entropy compared to solids because gas particles are more spread out and move more freely.

Understand that when gases transform into a solid, the system becomes more ordered. This decrease in randomness leads to a decrease in entropy.

Conclude that the sign of ΔS for this reaction, where gases form a solid, would be negative because the entropy of the system decreases.

Summarize that the expected sign of ΔS for the reaction is negative, indicating a decrease in entropy as the system changes from a more disordered state (gases) to a more ordered state (solid).

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Entropy (ΔS)

Entropy, denoted as ΔS, is a measure of the disorder or randomness in a system. In chemical reactions, changes in entropy can indicate whether the products are more or less disordered than the reactants. A positive ΔS indicates an increase in disorder, while a negative ΔS indicates a decrease.

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Entropy in Thermodynamics

Phase Changes and Entropy

The phase of a substance significantly affects its entropy. Gases have higher entropy due to their greater freedom of movement and disorder compared to solids. When gases react to form a solid, the overall disorder of the system decreases, leading to a negative change in entropy (ΔS < 0).

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Entropy in Phase Changes

Gibbs Free Energy and Spontaneity

Gibbs Free Energy (ΔG) combines enthalpy and entropy to determine the spontaneity of a reaction. A reaction is spontaneous if ΔG is negative, which can occur even if ΔS is negative, provided that the enthalpy change (ΔH) is sufficiently negative. Understanding the relationship between ΔS and ΔG is crucial for predicting reaction behavior.

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Gibbs Free Energy of Reactions

Pratica correlata

Domanda del libro di testo

(b) How does the entropy of the system change in the processes described in Exercise 19.12?

Domanda del libro di testo

Would each of the following changes increase, decrease, or have no effect on the number of microstates available to a system: (b) decrease in volume

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Domanda del libro di testo

(c) In a particular spontaneous process, the number of microstates available to the system decreases. What can you conclude about the sign of ΔS_surr?

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