In a reaction involving 0.0300 M of I-, 0.0300 M of H2O2, and 0.00300 M of S2O3^2-, which of the following expressions correctly represents the rate of reaction?

• A. Rate = k[S2O3^2-]
• B. Rate = k[I-][H2O2]
• C. Rate = k[H2O2][S2O3^2-]
• D. Rate = k[I-][H2O2][S2O3^2-]

Answer: (B)

Verified step by step guidance

1. Identify the reactants involved in the reaction: I-, H2O2, and S2O3^2-.
2. Understand that the rate of reaction is often determined by the concentration of the reactants that are directly involved in the rate-determining step.
3. Recognize that the rate law expression is generally of the form Rate = k[A]^m[B]^n, where A and B are reactants, and m and n are the orders of the reaction with respect to each reactant.
4. Consider that the rate law is determined experimentally and reflects the reactants that influence the rate of reaction. In many reactions involving I- and H2O2, these two reactants are often involved in the rate-determining step.
5. Conclude that the correct rate expression should include the concentrations of I- and H2O2, leading to the rate law: Rate = k[I-][H2O2].