In the reaction 2 H2S + O2 → 2 S + 2 H2O, which species has the greatest rate of appearance?

• A. S
• B. O2
• C. H2S
• D. H2O

Answer: (D)

Verified step by step guidance

1. Identify the species involved in the reaction: reactants are H2S and O2, products are S and H2O.
2. Recall that the rate of appearance refers to how quickly a product forms, while the rate of disappearance refers to how quickly a reactant is consumed.
3. Look at the balanced chemical equation: \$2\ \mathrm{H_2S} + \mathrm{O_2} \rightarrow 2\ \mathrm{S} + 2\ \mathrm{H_2O}$.
4. Note the stoichiometric coefficients for the products: 2 for S and 2 for H2O. Both appear as products, but the question asks which species has the greatest rate of appearance.
5. Since both S and H2O have the same coefficient, consider the nature of the species: H2O is a stable molecule appearing in the reaction, while S is a solid product. The rate of appearance is typically measured for species in the gas or aqueous phase, so H2O is considered to have the greatest rate of appearance.