Predict the sign of ΔS for the following reactions. (a) Ba(s)+Cl2(g) ⟶BaCl2(s) (b) Na

step 1 When determining whether or not a process has a delta S that's positive or negative, we need to

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

Predict the sign of $\Delta S$ for the following reactions. $$ \begin{array}{l} \text { (a) } \mathrm{Ba}(s)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{BaCl}_{2}(s) \\ \text { (b) } \mathrm{NaCl}(s) \longrightarrow \mathrm{Na}^{+}(a q)+\mathrm{Cl}^{-}(a q) \end{array} $$ (c) $2 \mathrm{NaHCO}_{3}(s) \stackrel{\text { heat }}{\longrightarrow}$ $$ 2 \mathrm{Na}_{2} \mathrm{CO}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(g)+\mathrm{CO}_{2}(g) $$

Predict the sign of $\Delta S$ for the following reactions.
$$
\begin{array}{l}
\text { (a) } \mathrm{Ba}(s)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{BaCl}_{2}(s) \\
\text { (b) } \mathrm{NaCl}(s) \longrightarrow \mathrm{Na}^{+}(a q)+\mathrm{Cl}^{-}(a q)
\end{array}
$$
(c) $2 \mathrm{NaHCO}_{3}(s) \stackrel{\text { heat }}{\longrightarrow}$
$$
2 \mathrm{Na}_{2} \mathrm{CO}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(g)+\mathrm{CO}_{2}(g)
$$

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Key Concepts

Entropy

Entropy measures the degree of disorder or randomness in a system. It quantifies the number of microscopic ways that a system can be arranged, and an increase in entropy reflects a transition to a more disordered state, while a decrease indicates a move to a more ordered state.

Effect of Phase on Entropy

Different phases of matter exhibit different levels of molecular freedom. Typically, gases have much higher entropy than liquids or solids because the molecules in a gas move more freely and are more dispersed, which contributes significantly to the overall randomness of the system.

Entropy Change in Reactions

Predicting the sign of entropy change (?S) in a chemical reaction involves comparing the randomness of the reactants and the products. If the products are more disordered—such as a reaction that forms gases or dissociates compounds—the ?S is usually positive. Conversely, if the reaction results in a more structured, less dispersed state, the ?S is often negative.

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