Predict the sign of Δ5^∘ for each of the following reactions. (a) H2( g)+Ni^2+(a q) ⟶2 H^+(a q)+

step 1 Entropy is a measure of the disorder of the system. And so as the disorder increases, the entrop

Predict the sign of Δ5^∘ for each of the following...

Predict the sign of $\Delta 5^{\circ}$ for each of the following reactions. (a) $\mathrm{H}_2(\mathrm{~g})+\mathrm{Ni}^{2+}(a q) \longrightarrow 2 \mathrm{H}^{+}(a q)+\mathrm{Ni}(s)$ (b) $\mathrm{Cu}(s)+2 \mathrm{H}^{+}(a q) \longrightarrow \mathrm{H}_2(g)+\mathrm{Cu}^{2+}(a q)$ (c) $\mathrm{N}_2 \mathrm{O}_4(\mathrm{~g}) \longrightarrow 2 \mathrm{NO}_2(\mathrm{~g})$

Predict the sign of $\Delta 5^{\circ}$ for each of the following reactions.
(a) $\mathrm{H}_2(\mathrm{~g})+\mathrm{Ni}^{2+}(a q) \longrightarrow 2 \mathrm{H}^{+}(a q)+\mathrm{Ni}(s)$
(b) $\mathrm{Cu}(s)+2 \mathrm{H}^{+}(a q) \longrightarrow \mathrm{H}_2(g)+\mathrm{Cu}^{2+}(a q)$
(c) $\mathrm{N}_2 \mathrm{O}_4(\mathrm{~g}) \longrightarrow 2 \mathrm{NO}_2(\mathrm{~g})$

Key Concepts

Stoichiometric Considerations in Entropy

Evaluating the stoichiometry of a reaction involves comparing the number of moles and phase of each species on both sides of the equation. When a reaction has an increase in the number of moles of a high-entropy phase (like gas) or a decrease in a low-entropy phase (like solid or highly organized aqueous ions), the overall entropy tends to increase. Conversely, a decrease in gaseous moles or an increase in highly ordered species generally results in a negative entropy change.

Entropy Change

Entropy change (?S) reflects the change in the number of accessible microstates or the degree of disorder for a system during a reaction. When predicting the sign of ?S, one considers whether the reaction leads to a gain or loss in randomness and energy dispersal. A positive ?S means the products are more disordered than the reactants, while a negative ?S indicates a decrease in disorder.

Effect of Phases on Entropy

The phase of a substance greatly influences its entropy: gases have higher entropy due to greater molecular freedom, liquids have moderate entropy, and solids have the lowest because of their structured arrangement. In reactions, changes that involve the formation or consumption of gaseous species generally lead to significant changes in entropy, with production of gas increasing disorder and consumption reducing it.

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