Which is a convenient synthetic method for the preparation of \(\mathrm{SO}_{2}\) ? (a) \(\mathrm{S}_{8}(\mathrm{~s})+8 \mathrm{O}_{2}(\mathrm{~g})+\) heat \(\rightarrow 8 \mathrm{SO}_{2}(\mathrm{~g})\) (b) \(2 \mathrm{SO}_{3}(\mathrm{~g})+\) heat \(\rightarrow 2 \mathrm{SO}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g})\) (c) \(\mathrm{FeSO}_{3}(\mathrm{~s})+\) heat \(\rightarrow \mathrm{FeO}(\mathrm{s})+\mathrm{SO}_{2}(\mathrm{~g})\) (d) \(\mathrm{H}_{2} \mathrm{SO}_{3}(\mathrm{aq}) \rightarrow \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{SO}_{2}(\mathrm{aq})\)

When synthesizing a chemical like sulfur dioxide (SO2), it's essential to consider the reaction conditions that will lead to an efficient production.

For a reaction to be effectively carried out, factors such as temperature, pressure, and the physical state of reactants (solid, liquid, gas, or aqueous) must be optimized. For instance, the reaction between elemental sulfur (S8) and oxygen (O2) to form SO2 necessitates the application of heat to overcome the activation energy barrier and facilitate the reaction.

The direct heating of iron(II) sulfite (FeSO3) spells out a clear pathway to SO2 without needing additional reactants, which simplifies the procedure. The ease of controlling the reaction by simply varying the temperature makes this method preferable in terms of reaction conditions. Furthermore, the physical state of the reactants and products—solids and gases, respectively—allows for easy separation and collection of SO2.

The feasibility of chemical reactions is determined by several criteria, including energy requirements, reaction rate, equilibrium position, and the convenience of obtaining reactants.

When selecting the most practical method of synthesizing SO2, the trade-off between the energy required to initiate the reaction and the ease of handling the products must be assessed. For example, decomposing sulfur trioxide (SO3) to SO2 and O2 might seem advantageous because there are no solid by-products, but the need for heat makes this less attractive as it implies a reverse reaction that is not naturally favorable.

The reaction of aqueous sulfurous acid (H2SO3) to produce SO2 is also feasible, but it yields aqueous SO2, which is less convenient to collect. The thermal decomposition of iron(II) sulfite, however, releases SO2 gas directly into the atmosphere, making the reaction straightforward both in theory and practice. The iron(II) oxide produced is a solid, which can be easily separated from the gaseous SO2.

The preparation of gases in a chemistry lab often involves decomposition reactions, displacements, or other types of reactions where a gas is one of the products.

For the production of SO2, methods that generate gases directly and in a pure form are usually preferred. In option (c), the decomposition of iron(II) sulfite upon heating is a classic example of a solid-gas reaction where a desired gas is produced along with a solid by-product.

The thermal decomposition method is advantageous as it yields SO2 in its gaseous state, which can be easily captured and purified if needed. Techniques such as using a drying agent or passing the gas through a series of tubes to ensure its dryness and purity are often employed post-reaction to obtain the gas in its most usable form. This method's simplicity and directness exemplify why solid-gas reactions are a mainstay in the preparation of gases in chemistry labs.