Predict the sign of ΔS for the following reactions. (a) The sublimation of I2(s) (b) CO(g)+2 H2(

step 1 For a chemical process, we can determine the sign of delta S by monitoring two things. If we hav

Predict the sign of ΔS for the following reactions. (a) The...

Predict the sign of $\Delta S$ for the following reactions.
(a) The sublimation of $\mathrm{I}_{2}(s)$
(b) $\mathrm{CO}(g)+2 \mathrm{H}_{2}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{OH}(g)$
(c) $2 \mathrm{Na}(s)+\mathrm{Cl}_{2}(g) \longrightarrow 2 \mathrm{NaCl}(s)$

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Key Concepts

Entropy

Entropy is a measure of the disorder or randomness in a system. It reflects how energy is dispersed at the molecular level and is central to determining the direction of spontaneous processes.

Phase Transitions

Different physical states have distinct entropies; for instance, gases have much higher entropy compared to liquids and solids. Changes from one phase to another (such as sublimation, where a solid becomes a gas) significantly alter the disorder and thus the entropy of the system.

Effect of Gaseous Molecules on Entropy

Gaseous molecules inherently possess higher entropy due to their greater freedom of movement and the large volumes they occupy. In chemical reactions, an increase in the number or production of gaseous species typically results in an increase in the system’s entropy.

Reaction Stoichiometry and Molecular Count

The overall change in entropy during a reaction can often be predicted by comparing the number and type of particles (especially in the gas phase) on the reactant and product sides. Reactions that involve a reduction in the number of gas molecules usually lead to a decrease in entropy, while those that increase the number of gas molecules tend to increase entropy.

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