Which of the following reactions is predicted to be...

Which of the following reactions is predicted to be product-favored? (a) $\mathrm{Zn}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{aq}) \longrightarrow \mathrm{H}_{2}(\mathrm{g})+\mathrm{ZnCl}_{2}(\mathrm{aq})$ (b) $\mathrm{MgCl}_{2}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{aq})$

Which of the following reactions is predicted to be product-favored?
(a) $\mathrm{Zn}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{aq}) \longrightarrow \mathrm{H}_{2}(\mathrm{g})+\mathrm{ZnCl}_{2}(\mathrm{aq})$
(b) $\mathrm{MgCl}_{2}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{aq})$

Key Concepts

Reaction Equilibrium

Reaction equilibrium describes the state in which the rates of the forward and reverse reactions are equal, meaning that the overall concentrations of reactants and products remain constant over time. In the context of product-favored reactions, the equilibrium position lies significantly towards the products, which is often quantified by a large equilibrium constant, indicating that a small perturbation can shift the reaction back to the starting materials.

Gibbs Free Energy

Gibbs free energy (?G) is a thermodynamic quantity used to predict the spontaneity of a reaction. A negative ?G indicates that a reaction is exergonic and will proceed spontaneously toward the formation of products under standard conditions. This concept is crucial for determining whether a reaction is product-favored, as a sufficiently negative ?G suggests that the overall process releases energy and is thermodynamically favorable.

Redox Reactions

Redox reactions involve the transfer of electrons between reactants, with one species undergoing oxidation (loss of electrons) and another undergoing reduction (gain of electrons). The spontaneity of a redox reaction can be predicted using standard electrode potentials, where a reaction with a favorable potential difference is expected to proceed towards the products. This concept is central to many reactions involving metals and acids, where electron transfer drives the formation of products.

Solubility and Precipitation Equilibria

Solubility and precipitation equilibria concern the solubility of compounds in a given solvent and the conditions under which a precipitate forms. When a product of a reaction is only sparingly soluble in the reaction medium, its removal via precipitation can shift the equilibrium position towards further product formation. This principle is used to assess whether certain reactions will be product-favored by considering the solubility products and how they affect the overall reaction dynamics.

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