How do you propose a mechanism for this reaction:
18H(+) + 4S2O3(2-)-->SO3(2-) + 7S + 9H2O
where the rate law:
rate=k[Na2S2O3] with first order respect to Na2S2O3...
To propose a mechanism for the given reaction, we need to consider the stoichiometry and rate law provided. Based on the rate law: rate = k[Na2S2O3], we know that the reaction is first order with respect to Na2S2O3. This means that the rate of the reaction is directly proportional to the concentration of Na2S2O3.
One possible mechanism for the reaction could involve multiple elementary steps. Here's one proposed mechanism to consider:
Step 1: S2O3(2-) + 2H(+) → H2S2O3
Step 2: H2S2O3 + H(+) → S2O3(2-) + H2O
Step 3: 2H2S2O3 → SO3(2-) + S2 + 3H2O
Let's analyze this proposed mechanism:
Step 1 involves the reaction between S2O3(2-) and H(+) to form H2S2O3. This step is the slowest step and thus determines the overall rate of the reaction.
Step 2 involves the reaction between H2S2O3 and H(+) to regenerate S2O3(2-) and water (H2O).
Step 3 involves the decomposition of two molecules of H2S2O3 to form SO3(2-), S2, and water (H2O).
The overall balanced equation for this scheme is the same as the given reaction:
18H(+) + 4S2O3(2-) → SO3(2-) + 7S + 9H2O
It's important to note that this mechanism is just one possible proposal, and there may be other mechanisms that are equally valid. The proposed mechanism should be consistent with the experimentally determined rate law. Experimental evidence, such as determining the reaction order experimentally or analyzing the reaction kinetics, is usually required to support a proposed mechanism.