I am supposed to create a "possible" mechanism for the reaction
2A + B --> 2C
when the rate law is Rate=k[A][B]^2.
This mechanism can include any letters (but must obviously include As, Bs, and Cs). Preferably it should be 3 or more steps including at one slow (or rate determining) step, at least one fast step, and at least one fast forward & reverse step.
I have puzzled with it for awhile and cannot find any that work...help?
To devise a possible mechanism for the given reaction, it's important to understand the rate law and the key elements of a reaction mechanism.
The rate law for the reaction is stated as Rate = k[A][B]^2, indicating that the rate of the reaction depends on the concentrations of both A and B raised to their respective stoichiometric coefficients.
When designing a reaction mechanism, it's helpful to consider the following principles:
1. The overall stoichiometry of the reaction should be maintained.
2. The sum of the elementary steps should equal the balanced equation for the overall reaction.
3. The slowest step in the mechanism should determine the rate law.
With these principles in mind, let's try constructing a possible mechanism:
Step 1: Slow (rate-determining step)
A + B → C (formation of an intermediate complex)
Step 2: Fast
C + A → 2C (regeneration of C)
Step 3: Fast
C → B (conversion of C to B)
In this mechanism, the initial collision between A and B in Step 1 is the slowest (rate-determining) step, as it follows the rate law dependency on [A][B]^2.
Now, let's analyze the overall reaction:
2A + B → 2C (overall balanced equation)
Looking at the mechanism, we can see that the stoichiometry is conserved since the number of A and B molecules are equal on both sides of the reaction.
Overall, the proposed mechanism abides by the given conditions, including a slow step, fast steps, and a fast forward and reverse reaction. However, it's important to note that this mechanism is only one possible solution, and there might be other valid mechanisms that meet the criteria as well.
To create a possible mechanism for the given reaction with the rate law Rate=k[A][B]^2, we need to consider the stoichiometry of the reaction and the proposed rate law.
One potential mechanism that satisfies the given requirements is as follows:
Step 1: A + B --> C (fast)
Step 2: C + A --> 2C (slow)
Step 3: C + B --> D (fast, forward)
Step 4: D --> C + B (fast, reverse)
Let's break down this mechanism and see how it fits the given rate law.
In Step 1, A and B combine to form C in a fast reaction. Since the rate law does not involve C, this step is unlikely to be the rate-determining step.
In Step 2, C reacts with A to form 2C in a slow step. The stoichiometry aligns with the overall reaction. The rate-determining step often involves the reactants in the same ratio as the overall balanced equation.
In Step 3, C reacts with B to form D in a fast forward reaction. This step is required in the mechanism since D is not present in the overall reaction.
In Step 4, D decomposes to reform C and B in a fast reverse reaction. This step is necessary to complete the catalytic cycle and regenerate the reactants.
By combining the rates of the rate-determining step (Step 2) and the fast steps (Steps 1, 3, and 4), the overall rate law "Rate=k[A][B]^2" can be obtained.
It is important to note that the proposed mechanism is only one possible solution and may not be the only valid one. Experimental evidence or additional information about the reaction may be required to validate the mechanism.