The values of ΔS^1 in Table 13-5 are generally positive or are only slightly negative. Why shoul

step 1 This question asks us to consider the equation delta G equals delta H minus T delta S. Why is it

The values of ΔS^1 in Table 13-5 are generally positive or...

Key Concepts

Entropy

Entropy is a measure of the disorder or randomness in a system, reflecting the number of ways the system’s components can be arranged. In chemical reactions, the entropy change (?S) indicates how the organization of molecules varies from reactants to products, which is a fundamental aspect in determining the feasibility and mechanism of a reaction.

Translational Entropy

Translational entropy refers to the entropy associated with the movement of particles through space. When free molecules come together in a reaction (especially in association or bimolecular reactions), they lose independent translational motion, which results in a large negative entropy change. This is why ?S^t values, which capture this aspect, can be quite negative during the formation of a transition state or complex.

Reaction Mechanism and Entropy Changes

Different reaction steps or mechanisms can exhibit varying entropy changes based on how they affect molecular freedom. In cases where only slight structural reorganization occurs without significant loss of independent motion, the resulting entropy change (like ?S^1) might be positive or only slightly negative. In contrast, mechanisms that involve the association of two separate entities typically incur a substantial loss in translational freedom, thus leading to more negative entropy values.

Solvation Effects

In solution chemistry, the way solvent molecules reorganize around reactants or during the formation of an activated complex can also affect the overall entropy change. Minor reorganization of solvent molecules around a single reactant (as in unimolecular changes) typically does not reduce entropy as dramatically as the formation of a complex from two or more independent species, where the overall order is significantly increased, resulting in more negative entropy contributions.

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